play tf2center/faceit (and don't get discouraged if you do shit which you and everyone else was at some point) and watch a few videos to try understand the basics of 6s flow
pugchamp is a bad idea unless you're experienced, mixchamp is dead
when you can try to sub/merc for a team to get an idea of more serious play, make some friends, join dmixes, play a season when you can with people your skill level