Welcome maxmoefoe,
Here is a quick explanation on: STEEM Power VS STEEM
Steem power is like karma - you are rewarded for making good posts and for upvoting other people's posts (known as curation).
Steem power is normally kept in your account and cannot be traded.
The more STEEM power you have, the more influencial you are on STEEM - your articles and votes will be worth more.
If at any point you want to start trading your power for fiat money (eg, USD), you will have to power down your account.
Power downs take about 13 weeks to complete. What you get is a tradable form of STEEM Power, called STEEM. This can now be exchanged on any exchange that supports it.