You have to post. After 90 days, your account should activate and you can earn I think it's 2NP$ a post that isn't spam. Be careful though, if you spam, they will revoke this privalige and you won't be able to earn points for posting, I should know, I'm still trying to speak with Mark, but he seems to be either very busy (which is understandable) or ignoreing me.
You can sell things in the Market Place forums.
Hope this helps.