You can earn both STEEM and Steem Backed Dollars (SBD) from your posts on STEEM-based apps like Steemit and Dtube.

SBD is good for $1 worth of Steem if ever you decide to convert it. You can also trade it on an external market, which is the better option at the moment since it's trading for over $4 (anything over $1 is added profit). The whole purpose of SBD is, at least in theory, to make a more stable currency, pegged to the US dollar, that would be a more attractive option for businesses (online retailers) than your typical crypto-currency, which can fluctuate by more than 5% per day. Obviously, it hasn't succeeded thus far at keeping the dollar peg as, like I mentioned earlier, it's currently trading on external exchanges, such as Binance, for over $4.

Steem, the actual currency of the Steem- blockchain, can be "powered up" into Steem-Power (SP), or "vested Steem". SP is what determines how much your vote is worth on Steemit and other Steem based apps. Everyday the same amount of Steem is awarded to content creators, based on who gets voted on by whom. The higher your SP the more percentage of the reward pool your vote awards.

Once you've powered up over 500 Steem, you get the option to choose your "voting power" every time that you vote (before that amount is reached, all your votes are cast at 100% voting power). When you go to vote, you'll see a "voting slider" that allows you to vote between 1 and 100% voting power (if your 100% upvote is worth $10, then your 10% upvote will be worth $1, it works on a linear growth line).

Each SP only has so much voting power, which decreases a bit with every upvote (or downvote), but it is forever renewed at a rate of ten 100% upvotes (or downvotes) per day, at a constant rate. So the maximum return on curation rewards (your reward for voting on content that receives further upvotes after you made your vote) comes with voting ten times at 100% or some equivalent (100 times at 10%, 1,000 times at 1%, etc.).

You can "power down" your SP whenever you decide to convert it back into Steem. This will divide the total SP by 13 and pay it out in 13 equal weekly payments to your account. You can end the power down whenever you wish and you can choose to power down any percentage of your total SP.

Hopefully this helps :)