To start playing with your NFTs you must stake them at first. After that, you'll see them appear in your inventory. Their health value will be equal to 1/4 of their maximum value.
For example, if you stake a tool that has a maximum available health value of 64, it'll have 16 health points when you stake it.
Item unstaking:
If you want to unstake your asset from the game, you'll have to repair it at first. Also, to unstake assets your energy must be greater or equal to 32. It takes 1 day before you get NFTs on your WAX wallet.