Steemit is much like Reddit, but you can get paid to post and upvote.

There are three units of currency in Steemit: Steem, Steem Dollars, and Steem Power

Steem Power:

Steem Power is like a passive income investment. You hold it for two years, and during that time you get paid in Steem just to hold it. I would recommend putting as much of your currency as you can into Steem Power.

Steem:

Steem is the basic currency in steem power. The biggest problem with holding it is that it's value will get diluted over time due to inflation. You should transfer it to Steem Dollars or Steem Power.

Steem Dollars:

Steem Dollars are like Steem, but their value never depreciates due to inflation. You will get paid 50% in Steem dollars from your content. It pays 10% interest yearly to hold. This is a lower rate that Steem Power.

You can either hold your Steem Dollars, exchange them to Steem and sell, or invest into more Steem Power. I personally prefer to invest more, but it's really up to you.

You can earn Steem Power, Steem Dollars, and Steem by upvoting content and more importantly posting your own content.