1. Which champs are easy to play?
Save your Blue Essence. There are free champions that you can try in the mean time to at least learn what role you want to play. It will take a while for you to figure out your preferred role, and it's better to have as much essence as possible so you can buy champions for that role instead of who looks fun but really isn't.
2. Where can I improve at the game?
Look up people on Youtube. People I watch are Foxdrop (jungler), Anklespankin (ADC/random), Phylol (ADC), SoloRenektonOnly (Top), and Prismal (Challenger ADC). The reason I suggest these people is that they explain what they are doing while playing, so perhaps you can see why they make the decisions they made. Prismal is really good at explaining things, but he can be a little overwhelming even for someone like me who has been playing this game for a few years, so maybe start with the others first.
Most of them talk expecting you to know certain things, like if I say Morgana Bind (her Q ability), they expect that you know what that ability does (it's a snare; a form of Crowd Control (CC) that stops your from moving but you can still auto attack and cast abilities), so you kinda need to know stuff before what they are saying makes sense.
If possible, get your friend to help teach you the game. Get in voice chat and let your friend explain things to you. If you need more help, I'd be willing to help teach you but since I'm in NA it might be difficult.
Otherwise I would recommend playing against bots for a bit (if you haven't been already) just so you can learn what each champions abilities do. It will take a while before you learn what each champion does, but learning that will help you learn the game quicker. I would also recommend looking up each champion to see what their abilities do. Even if you don't know everything that a champion does, having a basic understanding of them will help you.
There is a big difference between knowing what a champion does and being able to use them well, so don't be discouraged if it takes a while. I mentally understand how to play Zed and yet can't do it to save my life. Not all of us are meant to be able to play every champion.
3. What summoners should I take?
First thing first, summoners are a last resort. This is a common mistake new players make because the tutorial does a bad job explaining. You don't want to be using your summoners to get to lane faster. If you are 500 hp out of 600 hp, DO NOT use heal summoner spell. I know that's what the tutorial teaches, but that's not how it should be used. Instead, you want to be using them to survive a fight or catch up to a low health enemy to finish them off.
Summoner spells have long cooldowns because they are very strong. Generally, everyone takes Flash because it allows you to instantly dodge abilities that would kill you or to instantly get in range to finish someone else off. From there, it depends on the champion you are playing, the lane you are in, how you plan to play, etc. Again I highly recommend going into a bot game and trying out different spells.
4. is it not good? What items should I buy first?
Champion builds are something you learn over time. If you don't know what to build, I recommend looking up your champion on Champion.gg and just building what they recommend. There is a reason these items are built, but it's hard to explain because it depends on each champion, who you are against, who is your biggest threat, etc.
There is about to be a big change to ADC items (items that Sivir uses), so this information will only be useful for a little bit, but for Marksman, generally you want to build BF Sword, Zeal, basic boots, finish Zeal item (getting either Shiv, Rapid Fire Cannon, Phantom Dancer, or Runaan), upgrade boots, then finish the BF into Infinity Edge or Essence Reaver. That is considered the core items for most Marksman/ADCs. If you build BF, Zeal, Shiv, and IE in that order every game regardless of markman champion, you'll be fine.
5. Should I start playing ranked or not?
Personally I would say no. People take ranked very seriously, and if you don't know what to build, what runes to take, what each champion does, etc, then they will think you are trolling and will report you or flame you.
If you do play ranked, you will start around Silver, probably lose quite a few games, and eventually fall into Bronze where it will be harder to get better at the game because no one down there seems to understand the game/don't take it seriously.
My recommendation is to play against bots for a while, because they will help you learn the basics of what each champion does without needing to worry about causing people to lose games. After that, go into normal games. You've been playing against people in Twisted Treeline already, so you already sorta know what to expect
While playing against bots, you should learn a few things.
Firstly, you want to practice last hitting the minions. Last hitting means dealing the last bit of damage needed to kill it. If you last hit anything in this game, you get gold. Last hit a champion and you are awarded a kill + gold. Last hit a buff camp, and you are awarded that buff + gold. Last hit dragon and you earn a buff for your team + gold. Getting gold is the main focus in this game. Getting gold allows you to get items, which makes killing champions and taking towers/dragons/barons easier. Last hitting minions is the easiest way to get gold in this game, and learning to do that early will help you a lot as you play more. That is the number one thing people who are looking to get better at this game are told to do, so learning this early will give you a big advantage.
If you haven't already, learn to play with camera unlocked. I learned to play with locked camera, and then had to relearn how to play with it unlocked. Having it unlocked allows you to aim your skill shots at people off your screen. It also allows you to look at other areas on the map without needing to left click on the mini map. However, playing with it unlocked requires that you move your mouse much more to constantly make sure your camera is in a good place while also making sure you are moving your champion around as well. I recommend going into the game settings and lowering the camera move speed to 50 if not lower, cause otherwise your camera will fly halfway across the map if you slightly touch the side of the screen. Go into the Practice tool (in client, click Play button, click Training, then click Practice tool), and try moving around with it unlocked, then try last hitting minions while moving around. After it feels better, go into bots and try playing a whole game with it unlocked.
Lastly, learn to level up abilities with Control and self cast abilities with Alt. Being able to level up an ability mid fight might be the difference between a kill and an enemy escaping with 10 hp. Additionally, many champions have shields or heals that can be targeted to an ally or yourself (Janna shield, Lulu shield, Karma shield). If you are casting it on an ally, you have to click that ally. But if you want to cast it on yourself, you can instead just hold alt and hit your shield button and it will automatically place it on you. It is much quicker to do it that way and will save yourself from accidentally misclicking when you meant to protect yourself.
Building up muscle memory in this game will make your life easier, so try to learn these things now while everything feels weird so that it becomes normal the more you play.
is typically a must, unless your jungle, then it is 
. The rest depend on role and intent; 
to kill, 
for the movement speed-reliant, 
is optimal on marksmen, 
to absorb damage, 
to gank or roam heavy play, 
for those cases against much cc is detrimental.
4.) LDR, is not a good first item. Typically grabbed for later into games, particularly if they have a strong tank. Try crit or attack speed items, like 
. Also, they tend to list "Essential Items" first before "Offensive Items" and such. Look at recommended stuff.
5.) NO. Stick to normals and learn the ropes before you try anything like ranked.
, 
) and then pick items strategically from there. Also! boots are very important. You don't need to necessarily upgrade them first, but having basic boots and upgrading them by mid game is a good idea.
. He's a tank who's going to have loads of health late game and is probably going to buy armor against you. Your lord Dominick is probably a good idea since it gives %bonus armor penetration and a passive that is going to make you do more damage the more health he has more than you. It is however not a good buy as first item cause 1. You lack attack damage for the bonuses the item offers to matter 2. Sion still has to buy armor.. So you have nothing to penetrate yet xD 3.Sion still doesn't have this much more health than you so the passive giving more damage the more health difference basically doesn't apply.
If you have absolutely no skill expression other than "Run to target," then these guys are your best friends
