try to learn how to play with 2 characters from each class. sometimes the characters you want to play, end up getting picked so you need a few back up plans just in case
Just have fun and try all the characters, dont worry about being good That's not the point unless you play ranked, just have fun and always work toward improvement working on one shortcoming at a time until you play as good as you want
If you want to get a good ranking, don't play comp until you actually understand the game. (Positioning, team comps, counters, strats) being a certain level doesn't mean you understand these things so ignore people who say "wait until xxx level"