This is my attempt to explain it to uninitiated:

Bitcoin pays miners with a reward when they solve a cryptographic puzzle. (Objective proof of work)
Steemit gives a reward every 24h on the best content based on votes. (Subjective proof of work)

Rewards starts on July 4th. Until then it accumulates for that Big Day.

The price of STEEM is determined on the market against other cryptocurrencies like bitcoin is. A Steem Dollars(SD) is always worth $1 of STEEM and will start trading on July 4th. Since it has a stable value it will be valuable for traders.

To protect your Steem from the inflation(the reward) and gain more voting power(and curation rewards), you can power up your Steem and then have STEEM POWER.

STEEMPOWER(SP) can be converted back into STEEM in 104 equal weekly payments.

Reward from content creation: 50% SD and 50% SP.
Reward from curation: 100% SP
Reward from mining: 100% SP