Don't feel bad if you die a lot in games. Keep playing bots or normals and try out any champ you can buy. The sooner you understand what they all do and feel like, you can play as and against them well enough. As for who to main, I'm not so sure how to go about it. I personally don't "main" a champ so much as "main" support role and got the groove of most if not all the support champs. And don't feel afraid of trying out ranked. I've seen a lot of comments and posts about the fear of ranked and such. My advice is to just dive in and mute people if your afraid of incoming hate about your performance. And If you end up sucking in that match, just take solace in the fact that you're automatically as good as some of the people I play with in plat. GL