Steam Card €20

Log in to your Steam account.
The current available balance is displayed at the top right, next to your profile name.

Go to https://store.steampowered.com/account/redeemwalletcode and log in if you haven't already done so.
If you don't already have a login, you will need to create a Steam account first.
After logging in to Steam, enter your unique wallet code in the 'Steam wallet code' field.
Click Continue to add the balance to your account.
The amount of money from the Steam wallet code will now be added to your Steam wallet balance.
The current available balance is displayed at the top right, next to your profile name.

When you get to the 'View and buy' step during checkout, click on 'My Steam wallet' as your payment method.
The cost of the item you buy and the associated tax will be paid with your Steam wallet balance.

Note: If you have never added Steam wallet funds to your account before,
you may be asked to enter your current address so we can determine the correct currency.

The Steam gift card is valid for up to 12 months after activation.

For terms and conditions, visit https://store.steampowered.com/subscriber_agreement/

Go to https://help.steampowered.com for help with your problem.
Choose the most relevant option on the page.
The help site will then help you solve the problem yourself or send a help request to the Steam Support team.