Difference between Steem , Steem Dollars (SBD) and Steem Power (SP)

I will try and explain in a simple short way the difference between Steem , Steem Dollars (SBD) and Steem Power (SP)
Steem: Steem are basically the bricks that make up the other two forms of money within the system which are Steem Dollars (SBD) and Steem Power (SP). It has value which is in open market but it's highly volatile and has no practical use in the steemit ecosystem.
Steem Dollars (SBD): Steem Dollars (SBD) are the currency of the steemit economy just like the US Dollar.It's the primary medium through which people send and receive value and it has practical use in the steemit ecosystem.
you can now sell SBD on markets like Poloniex or bittrex by exchanging it (to BTC or other cryptocurrency supported by the platform )
Steem Power (SP): Steem Power (SP) is the long term investment,it's like a promise that for every unit of SP you will receive steem unit if you decided to cash out '' called Powering down '' it's usually take long time to be done (a hundred and four weeks !!!) they divide your total steem power by 104 weeks and you receive weekly payment so if you decided to not to power down they give an interest over the year to make people keep their steem power and that's the long term investment.
I will make a post about how to cash out your steem dollars and exchange it on poloniex market exchange so if you are interested follow me