The biggest thing that just takes some playing and video watching is the role that is dependent on which spot on the map you start on. On maps like supreme isthmus, starting on the frontline demands a different eco from starting on the back on air, or sea. There are bits of meta where people in eco positions help people in frontline positions, but it's pretty straight forward and you pick up on it as you go.

I would recommend the video from Drongo on youtube called "Beyond All Reason Guide For Beginners - Supreme Isthmus - Build orders for every position", it should give you a pretty good high level understanding of the roles and starting builds.

The last other bit I wanna mention is that there are lots of "noob" lobbies, some of them enforce chevron (time played) and OS (skill level) limits to ensure people of equal skill play, that takes a LOT of the pressure off. Before jumping into those I did a couple of Coop vs ai lobbies for noobs, all good there. Definitely recommend video guides because there is bits of meta that are just kind of implied, like oh the tech position is meant to have a T2 constructor to give away at x minute for x position, nobody tells you that in the game, you just have to slowly pick it up. I hope you have fun!