ELI5 : Steemit

Steem is like an Amusement Park.

You use Fiat money to purchase Steem. These are your tokens to play. 

You can transfer your tokens for either Steempower or Steemdollars.

SteemPower

The more Steempower you have the more influence you have on the rides being built. If you have a lot of Steempower than your upvotes are worth more, in turn content creators, ride builders, will more likely tailor their posts for you so you will give them votes. 

SteemDollars

SteemDollars are what the ride goers pay the ride builders for creating content tailored for their individual needs. Once they ride builders have SteemDollars they can use it as payment for their services, hold it for a while as they will get interest on it, or reinvest it back into the park so they can have other builders curate more content for them.