Where the heck do I start?

Hello, all. I recently got back into this game after seeing the article about how this game still has a competative scene. I finished most of the campaigns in my youth and have (imo) a decent grasp of core mechanics. My question is what's the best avenue for starting to play against others without getting just heartbreakingly stomped. The AI is ok practice but I notice the AI at any difficulty doesn't play anything like a human player. I can look at the lobby screen on steam but I cant make any sense of any of it.

Basically I want to know the best way to play casual/beginner games to get into the rythm of online play.