Steam allows you to purchase gift cards, but because it's an entirely online store, you have to activate the cards with a code first. Redeeming these codes in the Steam Store will add the monetary ...

Access the Steam platform and navigate to your account’s wallet section. Locate the option to redeem a wallet or gift card code and enter the Steam wallet codes provided with the purchased Steam ...

and then choose ‘Add funds to your Steam wallet’, followed by ‘Redeem a Steam Gift Card or Wallet Code’. While this is how most people add funds to their accounts, you can also add games ...