Steem is a Cryptocurrency coin like BTC. if you have 30 steem, thats worth like $60.00 USD because each steem is worth like $2.00 right now. but next week steem could be worth $3.00 so you will now have $90.00 USD. Thats how STEEM works. Now STEEM POWER is what you use only on Steemit.com , you take your STEEM and Power Up so you have a greater influence on the site and earn more, and give more when you upvote. Now you can always Power Down your STEEM POWER and turn it back in to STEEM but it happens in 13 payments, one a week. So thats a good thing if the STEEM continues to rise in USD. I hope that makes sense, and I believe thats pretty accurate as far as everything goes.