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If you’re completely new to the competitive scene, i would suggest you start by having a look at some youtube videos (or find written guides on google or something) about the very basics (rules and class limitations, objectives etc.) of the format you would like to play (4v4, 6v6, 9v9 aka highlander) although i didn’t watch any myself when i started, i’m pretty sure there’s plenty to find. With that being done you can additionally watch some class tutorials, like rollouts for any map, positionings, prioritization of objectives, for starters you can stick to your mostly enjoyed class, but you’ll need to learn how the other classes work aswell to understand the flow of the game, to develop teamwork, which will be getting more of a major subject as you get more into it and eventually climb higher in divisions.
Once you’re confident with that you should come together with a bunch of like-minded people, learn all the stuff above together, and get right into the game, from there it’s about practice.
Since you’re from the US i would also suggest you try finding a team on http://www.ugcleague.com/ or at least ask their forums for help aswell, UGC is more focused on america and should be easier for you
If you want you can check out http://rc.tf2center.com/ aswell, its a lobby-based matchmaking site with quite a lot of beginners, you can also try making friends there, ask them to play together some time, tell them you’re new to this stuff and you’d like to get into it etc.
You’ll meet some dicks there too though, just don’t be too sensitive about being called a noob or whatever and keep practicing
HF GL

cheers, im off to bed, 4am in germany zZzZ