Futures and promises are words that describe a certain type of situation. In this situation, one person makes a promise to do something, while another person agrees to help. The first person is called the "promiser" and the second person is called the "future holder".
For example, imagine your friend wants to borrow some money from you. You make a promise to give them the money at a certain time. Your friend agrees to help out and is now the future holder. Your friend is counting on you to keep your promise, and so you need to do whatever it takes to make sure the money is given at the agreed time.
When the promiser keeps their promise and the future holder receives what was promised, the future and promise have been fulfilled.