Steem - is the basic cryptocurrency used to power this whole system. It’s like the bricks used to build Steem Dollars and Steem power. You can buy and sell Steem, speculate on it’s price or convert it to Steem dollars and Steem power.
Steem Backed Dollars - or simply Steem Dollars are stable value pegged assets issued in the Steem.it platform.
SBD are pegged to the value of the USD and can be redeemed on the Steem.it platform for about one dollar worth of Steem. Holding SBD pays interest. SBD is always convertible to $1.00 worth of STEEM.
Steem power – Also known as SP in short, is basically a token symbolizing how much influence you have inside the Steemit platform. If you have a lot of SP your upvotes will count more and will award different authors SP and Steem dollars as well.
When Content creators receive rewards on the Steem.it platform they are made available in 50% Steem Power, which can be redeemed continuously over a period of 104 weeks, and 50% SBD which can be fully redeemed for Steem in a 5 day period. SBD can also be transfered on the Steem Platform and can be exchanged outside of the Platform.
Source :
https://www.cryptocompare.com/coins/sbd/overview/BTC
https://steem.io/getinvolved/steem-backed-dollars/
https://99bitcoins.com/making-money-with-steemit-steem-dollars-and-steem-power-explained/
Steem Dollar Ticker & Conversion
You can also watch this simple explanation for Steem, Steem Dollars, and Steem Power