Hey man! Welcome to the forum!
You can take a look at what different levels there are here: User Levels Explained
As far as what you can do to contribute - just read the forums! See what interesting topics come up, and if you feel you can contribute with your knowledge, go for it!
If you discover some interesting info regarding marketing or social media or any related topic, start a new topic and tell us about it. If you see a people are facing some problem you have a solution to, (maybe you can write a small piece of code or script that they can run to solve their issue?) you can post that too!
And there’s a very nifty search tool on the top right, so you can always see if your questions have already been asked, or whether your answers have already been said before.
Cheers, and see you around!