Both steem and sbd are an alt coin. You can turn them into bitcoins or trade them on the exchanges like bittrex. The value of SBD should stay about one dollar but the value of steem moves with the markets. Steem power has a powerdown time on it. when you start the powerdown every week it converts percent of steempower to steem. think it takes 13 weeks for full powerdown but its been a whilke so im not 100% on the length of time.
Im not sure if that helps much, if not let me know what part I need to explane better.
:D
cheers
RE: How to earn