Steam gift cards function similarly to gift certificates, 

and they may be used to buy games, software, hardware,

 and anything else you can buy on Steam.

You can make a straight online contribution to a friend or relative’s Steam wallet. 

Note: Your Steam account is used to send digital gift cards. 

You can easily and for free establish an account using your email address if you do not already have one.

The Steam Wallet is used for all Community Market purchases and sales. 

The money cannot be taken out or moved to a different Steam account, a bank account, or a third-party account.

Simply put, a gift card is a particular kind of prepaid card that has a predetermined value and may be used to pay for goods at a particular store.
It is explicitly stated in Steam’s terms and conditions that money cannot be withdrawn to a bank account or refunded once it has been added to a Steam Wallet.