Great video. So when I AUTHOR a post i earn STMdollars + SP. When i earn curation rewards i only earn Steem power. Steem can trade inside the steemit universe only on the internal market; from member to member. Steem does not earn interest.
Steem POWER earns interest and decays per day slightly since new steem in created daily and mainly converted into steem power. So i convert my Steem into SP via power up.
Steem power has no value except within steemit and takes 2 years or 104 weekly splits to power down into steem. Thus steem power is locked away for many many months before being able to be traded.
Steem dollars are the outside money market source to buy or sell steemit cryptocurrency. I sell some SteemDollars via external marketplaces for Bitcoin to buy or sell into real dollars...