How long have you been playing for? I'm going to assume not for very long given the way you wrote your post, so I'm going to assume you know absolutely nothing about this game and structure my advice accordingly.
The first thing I noticed by looking over your summoner profile is that you are not max level yet, and as such have yet to unlock a full suite of runes and mastery points. This is going to put you at a disadvantage against max level players by default. Runes are just that important.
The second thing I did was look at your match history, and it's all ARAM's. While I have nothing against ARAM's (they are quite fun), you learn next to nothing about how to actually play League of Legends properly in that context. What I mean by that is you don't learn how to play on Summoner's Rift, the primary game mode. If you have no interest in playing in on the Rift, feel free to ignore the rest of this post.
On an ARAM, you are stuck with a random champion, one with which you may or may not be comfortable on or even enjoy playing. You probably won't get to last hit many minions, as everyone is fighting for them, and given the limited amount of maneuverability on the murder bridge, you're going to get smacked in the face by a whole lot of skillshots (especially if you're a newbie and don't know how to dodge yet). This leads to a very (in my opinion) unsatisfying and boring game experience. (Again, from the perspective of a newbie who doesn't know what they are doing).
The REAL League of Legends experience (and I use that term loosely) is Summoners Rift. This is where you will actually learn the meat & potatoes of the game and how it is (again personal opinion) intended to be played. With that in mind, let's look at the most important aspects of playing on the Rift.
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Resources: At it's heart, League of Legends is a game about resources. By getting the last hit on a minion or neutral monster, you earn gold. This gold is, in turn, used to buy items to increase the power of your champion. It is IMPERATIVE that you learn how to farm on whatever champion you are playing, because whoever shows up to the fight with more stats is typically the winner.
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Objectives: Your team can have a million kills, you can get a back-to-back Penta, but if your Nexus is the one that blows up you still lose. That's because objectives are the most important part of this game. I cannot count the number of times I have seen team idle around mid lane, fighting over and over again while the side lanes are totally ignored, it breaks my heart. Towers are free global gold for your team, and are the most important objective, by destroying an enemy tower, your minion waves push further and further into enemy territory, destroying a tower also limits the enemy teams vision of the map, and makes invading the enemy jungle easier and (somewhat) safer.
By cracking the enemy teams Inhibitor turret, and then the inhibitor itself, you gain a TREMENDOUS amount of free pressure on the map because the enemy team is forced to commit one or more members to dealing with Super Minion empowered waves. If left unattended, Super Minions will easily overwhelm and destroy the rest of the enemy base (especially if you take top or bottom lane inhib, as that will make your minions focus-fire one Nexus tower rather than both if they are coming through mid).
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Vision and Positioning: The most often ignored aspect of the game, vision control and map positioning/awareness are how the Big Kids play this game. Poke comps and pick comps both excel at picking fights from the fog of war, as it's much easier to kill and enemy if they don't see you coming. There are plenty of guides available on how to ward properly, and I suggest you familiarize yourself with the ward locations that will give you the biggest bang for your 75g. If you know where the enemy team IS, you also know where they ARE NOT, and if you can see them while they can't see you, that means you get to pick the fight on YOUR terms, playing to YOUR teams win conditions. Once you force the enemy team to dance to your beat, they have lost control of the game.
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Team Composition: This is where your background in WoW actually puts you at something of an advantage. The easiest way to win is to pick a strong team comp, where every champion complements the other. Similar to how a 5 man dungeon group requires ye olde Tank, Heals, and 3 DPS, so to does a proper LoL team comp require a delicate balance of offense, defense, and utility. There is no hard and fast rule about what you should or should not play, however, and one of the joys of playing this game is iteration & experimentation, finding what works best for you and your team. My own general rule is this: crowd control wins games, especially in games involving inexperienced players. More often then not these games devolve very quickly into mindlessly teamfighting, so it's better to just have a comp that does that better than the other guys. I'll give an example comp (that's also a "theme" comp):
Top - 
Jungle - 
Mid - 
ADC - 
Support - 
I call it the 'Freljord lockdown comp' and it brings a stifling amount of crowd control to a fight, probably bordering on overkill, but that's the way I like to play. Every member of the team brings either strong slows or stuns, and you have multiple AoE CC ultimates that you can use to start a fight, disengage, or counterengage. Which brings me to....
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Fighting: Despite everything I have said previously about objectives, vision, etc. It all means absolutely nothing if you don't know how to actually throw down. The best time to pick a fight is when everyone is healthy, ultimates and summoner spells are available, and your whole team is grouped up to take a tower, dragon, or maybe even the big bad Baron. This is not always the case, as sometimes a fight will be a 2v2, 3v2, 3v3 etc. These fights are called skirmishes, and the best way to win them is to identify the squishiest target and blow them up while keeping your own squishies safe (ish). Typically this will be the enemy ADC or Mid laner, as carry type champions tend to avoid purchasing defensive items for as long as possible, instead relying on their team to get them out of trouble. When everyone is grouped up for a 5v5 though, things get a bit more complicated. My advice would be this: Don't jump the gun on your initiations, instead let THEM come to YOU and as soon as a prime target presents themselves by being out of position, jump them. This is why I myself prefer to play champions who can either counter a bad initiation and punish, it preys on the overly aggressive mentality of the typical League player.
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Mentality: A frustrated and emotional opponent is already defeated, you should stay calm and play a methodical game, outmaneuver your opponent around the map, and punish their mistakes. Team morale is HUGE and you should never reprimand a teammate for a mistake, instead laugh it off and just keep playing. I know this is a lot of information and some of it might be a bit over your head. I have been playing this game for years myself and look at the game in a very cerebral way. If you start to lose your cool, take a break, step away from yourself and look at the game objectively. Every mistake is an opportunity to grow as a player and you absolutely MUST fall flat on your face before you learn to fly. To guard your own mentality you should pick up a few champions for every role and learn them to the point that playing them becomes second nature. You should be COMFORTABLE while you are playing, not fumbling with a combo or abilities that you haven't yet mastered.
Finally, and perhaps most importantly, have fun! Remember that you aren't even max level yet, you have so much room to grow and learn so don't sweat the little stuff. EVERYONE sucks at this game when they first start, no exceptions. If you approach this game with a healthy, positive mindset and embrace failure rather than punish yourself for it, your confidence and mastery will grow exponentially.
