"Also their attacks are very slow?" Yes, their autoattacks are very slow because they don't build attack speed, though this isn't a problem because they usually rely much more on their abilities anyway. They usually want to do things like lock down potential threats or mitigate incoming damage which they do so through good use of their abilities. Or are you saying this as a possible downside for you, something you don't want?
"All I know that I suck as tank as I soak almost every single damage and die very quickly" This is an issue of knowing damage outputs and knowing how much damage a champion can conversely take, which is related to roles quite nicely. Right now, you say you play ADCs and ADC, as in a champ building a glass-cannon DPS build, is a champion who have a, quote-unquote, damage-absorption rating of "Minimal", generally you want to avoid getting hit at all. Knowing how much your champion can take at a certain time is something that comes from experience and you will learn it in time.
So if you want to avoid that for now and take a set of champions whose intentions are similar with "take as little damage as possible" you can go with the traditional Mages. You would play ranged damage, artillery if you would like, and want to do damage while avoiding being engaged on in teamfights. There's differences, your damage will work around cool-downs and you'll have to start worrying about mana to even do damage, and CS will be harder since your auto-attacks do little damage but you will also be able to CS without about getting stuck in close-range auto trading situations that you would with two melee champs, so you may find benefit in that.
"Well, which role do you think I should choose? I would like some recommended champs for that role." All that said, I would actually recommend you try out the free rotation instead because people seem to find that works for them. Being able to play a champion yourself should be the best way to figure out whether you'll have fun with them, more than whatever role they are supposed to be, while the champions that may be recommended to you may cost more IP than you currently have and it would probably suck if you bought an expensive champion that you didn't like and won't play.
are able to be devastating in early games while champs like 
and 
can just tear through teams in late games. However, as I am starting to become more and more experienced with the game, I noticed one thing, almost every new player chooses to be an ADC or they just choose 
(OP P.O.S They just spam his E and get the kills).
Anyway, I also learnt that having more than one ADC is not a really good thing. And since I am just level 12, I have no idea which role I should pick. Which role will be a good transition from ADC to that role? All I know that I suck as tank as I soak almost every single damage and die very quickly. Also their attacks are very slow?
Well, which role do you think I should choose? I would like some recommended champs for that role.
