Futures and options are different in a lot of ways.
If you read the snippet from Investopedia about futures -
Assume two traders agree to $100 on an oil futures contract. The buyer agrees to buy oil at $100 at expiry, and the sellers agrees to sell oil at $100. If the price of oil moves up to $105, the buyer of the contract at $100 is making money because they have an agreement to buy at $100 even though oil is currently trading at $105. The seller on the other hand is losing, because they could be selling at $105, but instead they agreed to sell at $100.
Since the agreed price is 100$, that becomes the price where one person turns his contract to in-money and the other out-of-money. The date is fixed (which is expiry).
How can you set an agreement with fx futures and set a fixed future price?
To answer this question - the Futures agreement would happen on the 100$ amount.
Another price that is important is the underlying asset's (in the example above - oil) trading price when you buy the contract. Based on whether the contract is in money (if the underlying asset price is already above 100$ at the time if buying the future contract), or out of money, the price of the contract would vary in the market.