I have 25 keys for free play and can't use them, someone help?

On the bottom right side, of the box the prize is in, next to the "i" in the teal circle, it will show if that prize can be played with keys. As well as how many you will need. Click a prize box with keys on it and when the game starts there will be a circle option to play with coins and above it a circle option to press with keys.

They arnt much to fuss about. More for just the fun of the game or to practice. If you win the shipping on key prizes are ridiculous.