Once you purchase the steam wallet code or gift card from officialreseller.com, it will be delivered to your email. In order to redeem your Steam Wallet Code, you will need to create an account at steampowered.com. The quick link to this page is here: https://store.steampowered.com/join/
WHAT CAN STEAM CARDS BE USED FOR?
You can purchase the following on steampowered website: