The contracts are 60-minute forwards; you are agreeing to buy/sell Bitcoin at the current price (determined by the CoinDesk BPI) but 60 minutes from now. At that time the Bitcoin is transferred from the seller to the buyer, and the strike price (denominated in $) is paid in Bitcoin at the current price. The net effect is that the seller nets a small amount of Bitcoin if the price falls, giving them an amount equivalent to the original exchange rate. If the price rises the buyer nets a small amount. This is essentially a way of locking-in the rate now if for various reasons (waiting on blockchain confirmation for example) you cannot immediately sell off a parcel of Bitcoin. This would be very useful to payment operators, ATM operators, and merchants, for example.
The order book right now is shallow and comprised of our own funds; however we are in the process of onboarding several interested parties so I know that will improve in time.
Showing more before signup is an excellent suggestion; if you are not averse to submitting an email address you can try the paper trading site with 100 fake Bitcoins at paper-trade-bitfuture.com . Thanks for the feedback!