When you post people can vote up your post. Its called upvoting. You can earn money from this, how much depending on how popular your post is. You can also earn money by voting on popular posts and by commenting if these too are upvoted.

Lastly if you did have a popular post which for example earned 100 dollars you would receive half this in steam dollars which are easily transferred to bitcoin and the rest in steem power which gives you more influence when you vote.

There is a lot more to it but thats a start :0)