Unique Features

To accomplish its goal of a decentralized social media platform that rewards its users, Steem.it has several unique features.

Three internal currencies: STEEM, Steem Power, and Steem Dollars

Steem.it uses three currencies to power its network: STEEM, Steem Power, and Steem Dollars.

STEEM is the basic currency unit of the Steem ecosystem – everything is valued in STEEM and it must first be acquired to enter or exit the steam network. It is traded on exchanges.

In order to be active on the platform, users must convert STEEM to Steem Power. This conversion ‘locks’ their STEEM – it’s not burned, just inaccessible while it’s being used as Steem Power. This is referred to as ‘powering up.’ The rate of conversion changes and can be found here as steem_per_mvest on the right.

Users can’t immediately convert Steem Power back to STEEM: they must submit their SP and receive weekly installments of STEEM over two years, similar to bond payments. This is referred to as ‘powering down’.

Steem Dollars are another token in the ecosystem. One Steem Dollar is redeemable for $1 worth of Steem at current market prices (.3 STEEM at time of writing). One can convert Steem Dollars to Steem within the Steem platform and then sell the Steem for a fiat currency on an exchange. The actual trade is delayed by one week: initiating the conversion means the Steem Dollar will become STEEM at the market price in exactly one week.

The blockchain issues these currencies in the form of payouts and broader inflation. The total supply of STEEM (including that locked up as Steem Power) doubles every year through reward payments on the platform and as payments to holders of Steem Power (those who have ‘powered up’). 10% of the doubling goes to reward creators and curators; 90% goes to holders of Steem Power in proportion to the amount of Steem Power they inidividually hold. Steem Dollars are also given out as reward payments.Here is a brief primer summarizing key aspects of the currencies.

I think It will help others better understand differences between STEEM, STEEM POWER and STEEM DOLLARS.
You can read more here:
http://www.smithandcrown.com/how-does-steem-it-work/