A good starting point will be the white paper published by the creators of this platform. Steem is not only a platform for rewarding directly the writers - this is just the tip of the iceberg - but more of a virtual economy based on the blockchain.

Put it very short, there are 3 types of rewards you can get: Steem, Steem Power and Steem Dollars. Steem is the base cryptocurrency, Steem Power can be obtained through Steem and it's more of a long term investment, Steem Dollar is the currency directly related to this publishing platform (Steem as a cryptocurrency can exist independently and traded independently, whereas the Steem Dollars can be obtain directly from posting here).

You can get Steem by posting relevant content and curating relevant content.

In a nutshell, that's what's happening.

I would suggest to start by posting a "Introduce myself" type of posts (do a search for that, there are plenty) and validate your account by tweeting the link of that post, making a screenshot of it and commenting with that screenshot on the "introduce myself" post.