New to LoL and forums

I'm new to this forum, and tbh I wasn't expecting to post here. A friend of mine has been into LoL lately and I don't really know much about it. I heard that it doesn't work on linux natively, are there plans for that in the future? My friend said it works on Mac and that shouldn't be too much different right?

I played once before a LONG time ago, and I remember that you had to like.. pick your character fast or someone else could take it. Is it possible to play the same character over and over without being forced into another? That's something that really bugs me

Also, any tips for a beginner? My friend said he wont even play with me until I get better hahaha