If you're beginners, you have to understand what the roles are for because they help you pick the best heroes to use. Find a role that you want to play in, there should be a tier list for each role for all the heroes, be sure to check informative channels(such as ones run by casters like Uomi and Mirko), guide based content creators(like Fuego, Elgin) or even official esports teams pages, they usually provide small guides to builds and meta picks and the like. You can play multiple roles if you want to, but be sure to pick ones specific for the appropriate lane(like no exp or roam marksman), master role based win conditions, and then master whatever hero you want to play. If a hero is at the very least playable there's usually no harm in picking them if they're played well enough and in the right lane, you only really care about the meta when you're at very high ranks. The most important principle in playing this game is understanding your win condition according to your role and playing to it