Hello, I am a bit new to this game

Not typically, but it does vary by ELO. Most often, a solid win is made by everyone on a team--and I know that sounds PC, after-school special kind of, but it's true; everyone has their places in the game, and their responsibilities. But, it usually comes down to the following:

Top lane: Top lane most often produces tanks, pushers, duelists, and the like, though it can foster assassins in the current meta. Typically, the most survivable champion goes here, which can be someone who's just tough, or someone with good escapes. Top lane is most often responsible for split pushing, or keeping lane pressure constant top, though they often contribute a lot to late-game teamfights, especially with them bringing Teleport a lot of the time. This lane holds a lot of Maokai, Ryze, Rumble, Sion, Zed, Shen, Diana, and so forth. Late game, a lost bot or mid can be handled by split pushing, which is where this lane comes in. If it's top vs top, then no problem, your team is allright. But if they send more than one person top-lane to kill you for good, then it gives the rest of your team space to take objectives like towers or Dragon. Top is this way because, of all the lanes, it features the greatest distance between the two towers, making it tough to escape a gank if you're too far.

Jungle: The jungle is maybe the most varied of all of the 'lanes', since the only real requirement here is the ability to keep yourself alive. Most often, this is through sustain, whether built in lifesteal or some other self-healing, but there are a lot of other bonuses. Tougher champs excel here, and heavy crowd control is great, as it will make your ganks potent. That being said, the jungle brings with it a high ream of responsibilities. First, you take Smite, always, and this gives you more objective control. You'll need to use this to secure or steal baron and dragon whenever possible, but it also helps you take your own camps and even counter-jungle. The most important part, though, is map awareness, or the art of knowing where and when to gank. It's tough, strategically, but you get good at keeping an eye on who's pushed out and who isn't, on when lanes will be pushed out, and using this this knowledge to gank or anticipate an enemy gank. Your biggest priority will be either mid or bot, depending on a lot of choices. Your instinct will be the lane that needs help, but an easy, easy win bot lane might be worth more than saving a shaky midlaner (and I say this as a midlaner). It just depends. A lategame monster like Cassiopeia or Vayne might weigh into this. The strongest junglers seem to be a mix of Lee Sin, Jarvan, and Vi--a good mix of tanky champions with good engage and mobility, good crowd control, survivability, and a general fit for everything. Popular choice include Sejuani, Udyr, Shyvana, Amumu, and Rammus.

Mid lane: This is usually where the AP carry goes, or the assassin in most comps. It's a safe-ish lane, with some caveats. It has bushes on both sides, not just one, and requires constant warding. Ideally, the midlaner will do this themselves, but... eh. Anyway, usually squishy champions go here, but they're almost always at least a bit ranged, and great at the later stages of the game. Going solo mid lets them farm quicker than anyone else, getting more gold and experience when done correctly. On the other hand, it can be easy for a midlaner to die by a gank or just an all-in before help can get there. But, in turn, if they make it okay to the end of the game or even get fed, they usually provide a lot to their team--high sustained or burst damage, target elimination, hefty crowd control, and so on. This makes them good at teamfights or fighting in general, as they can sometimes provide a lot of area damage. On the other hand, a lot of crowd-control reliant mids can always bring something to the game. Typical AP carries are Orianna, Morgana, Malzahar, Karthus, Kassadin, Ahri, Twisted Fate, and Syndra. Ap or AD assassins are often Katarina, Zed, Fizz, LeBlanc, Kassadin, and Talon. This being the shortest lane, smarter players will survive better hands down, but ganks and turret diving are a thing that can turn the tables on anyone.

Suport: Another vital role, support is often a thankless babysitting job that just doesn't get the recognition it deserves. It's often unwanted, as well, but can nonetheless make or break many games. On the other hand, a good support can give any single team the push it needs to go from bad to pretty good, or from great to excellent. Primarily, supports are just that, a role that takes less experience and money where possible while providing lane-safety and kill securing services to foster the AD carry they go bot with. This role includes a large mix of survivability, crowd control, and utility not seen elsewhere, but for this reason, a lot of support champs are also good mid. To this end, support is an easy role to learn and get into, but surprisingly difficult to get a good grip on. The responsibilities of the support include saving your ADC (where possible), helping to land kills, and warding basically wherever possible as often as possible. It can't be overstated that everyone on a team needs to ward--it is one of the single highest priorities in the game, in my opinion... but supports should be up there in warding from jump street, and denying enemy vision where possible. Other duties can be engaging on the enemy, whether early game bot or in later teamfights, locking down an enemy to save an ally or get the target killed, roaming to help other lanes once the mid-game begins, and generally just being a go to Maker of Happening Things, depending on champion. Engagers include Thresh, Blitzcrank, Leona, and Zyra, who are often crowd control monsters with target picking that also gives them good peel. Healers include Soraka, Sona, and Nidalee (to an extent) who hand out sustain and often bring extra utility, like Sona's speed up and ult, Soraka's silence (and dat ult) or Nidalee's free trap wards. And there are some generalists, like Nami, Janna, and Lulu, who provide a good general mix of everything.

AD Carry: Also called Marksman, the ADC is often considered the most important position in League, typically by the ADC themselves. Nonetheless, the carry earned its name for a reason, that being them taking your sweet ass to victory when everything goes according to plan. But before that, you need to carry them as a team. This role is sort of homogenous in type, that being ranged basic attackers, but it varies widely in execution. Most often you're looking for someone who scales well with AD, obviously, but beyond that it all comes down to playstyle, preference, and of course, team composition. There are champions here with better early games and better late games, and names you know of as pokers, all-inners, damage monsters, even burst 'casty' ADC's. They work well with and against certain types of supports (and other ADCs) and this interplay breaks down to complicated give and take moments where just about anyone can win, especially factoring in ganks. Bot is, of course, vital, but not just as a lane, but factoring in Dragon control. An early double kill bot, especially if those two are the enemy jungler and ADC, can mean a free Dragon, and that can win a game if you use it well. On the other hand, a lost bot doesn't always mean a lost game, but it isn't nice. After early game, being an ADC is still all about farming, but it's also about knowing when and where. Roaming bot to push is fine, but keep an eye on the enemy team as much as possible. A roaming jungler or assassin especially can already be counting you as another few hundred gold. But, once you get most or all of a whole build, there's no one in the game better at damaging, killing, or pushing towers. For straight up damagers, you most often utilize someone with a damage or attack speed steroid of some kind, like Draven, Kog'maw, or Sivir. They often have damaging abilities that can add burst to their kit, especially early game, but rely on attacks and modified attacks, with some utility to keep them in the game. Bursty ADCs often put a lot of stock into their abilities at all stages of the game, and are usually pretty solid, like Graves, Lucian, and Twitch. And though anyone can duel, some ADCs excel at this role like all others. For me, Vayne, Kalista, and Quinn are standout examples of deadly 1v1 killers, and all of them can have trouble early game.

The best games are when all the lanes come together, and when your team makes a good use of its strengths. Regardless of everything here, lategame can all come down to a single team losing its ADC before the last fight, or having someone push top all game, or having a bit too little luck in a grab for Baron.

I probably got a bit wrong, but I think I did okay on everything.

As for duelists, the top tier duelists (aside from ADCs like Vayne and Kog lategame) are probably Jax, Poppy, Udyr, Fiora, Vi, Irelia, Warwick, Olaf, Master Yi, and Trundle. Probably. With varying degrees of success, mind you. For dueling, there's probably not many in the game who can 1v1 a Jax when he farms and plays well. And I think Fiora's in a bit of a trouble spot, right now. But everyone has their strengths. Vi and Udyr are excellent junglers, with Trundle and Warick being not too far behind in my experience. Jax and Irelia are great top laners, as well, and both give a lot to skilled players. Master Yi, when played, is very easy to get used to, has a pretty mixed bag for his kit, and snowballs well if you start getting kills. It's recommended to take him into the jungle, but your ganks as Yi will be less 'help the lane get kills' and more 'help b getting kills yourself'. He also deals with true damage centered around his basic attacks, like Irelia and Vayne do.