I don't know why everyone is telling you to play this champ or that. But I'm not really on board with telling you to play Garen, Annie or whatever champ they think is "ez mode".
Annie for example, with all her simplicity is a champion I can never click with. I always feed on her. Azir on the other hand, despite being arguably the most difficult champion in the game, I was able to maintain a nice 53% win rate on him back when I mained him. Take these champion suggestions everyone is giving you with a grain of salt. The reason I can play Azir much better than I can play Annie despite Annie being by far the easier champion, is because I enjoyed playing Azir. I never enjoyed playing Annie.
This brings me to my point. You just haven't found the champions you click with yet. I've played almost every champion in this game at least once. I think there are like 4 I've never played on SR. What I've noticed is that there are champions that I click with after just a few games and there are champions that no matter how much I play them I can't get them at all. I always feed or end up not being able to do anything.
Annie, Kai'sa and Camille are just three examples of champions that despite how much I try, I just can't do shit with them. Something in their kits or play style just doesn't resonate with me and I do horribly every single time I play them. In contrast, the very first time I played Kayle, she clicked for me. I went like 10-4 my very first PvP game on Kayle. And to date, she is the champion I've had the most success on. I also clicked with champions like Malphite, Nasus, Leona, Nautilus, Nocturne, Vi, Shyvana, old Akali, old Irelia. Miss Fortune, Ashe and a handful of others.
What I would suggest you do is play as many champions as possible. Try them all. You will click with some of them and they will become your champion pool. 99% of League players have a champion pool that can range from one champion to as many as 20 champions. You have no need to learn how to play all of League's champions but you MUST find the ones that resonate with you most. The easiest way for you to know which champions might be for you is to ask one simple question.....was this champion fun to play? If the answer is yes, then there is a 90% chance that this is a champion you would become very proficient at. Also, you may not click with a champion on the first game. Shyvana is an example of this for me. My first game with Shyvana, I didn't get her at all but I knew liked her intended play style and she had some elements in her kit I enjoyed. By the 5th game with her, I figured her out and started doing very well on her. She went on to become my most played champion in season 8. So try each champion at least 5 times before you decide whether they are for you or not.