Steam Guard enable
- Click in the upper left corner on "Steam". In the following Drop-Down menu, select "settings".
- Under "Account" you need to click manage on the "Steam Guard account security...".
- Now you have to do is select "My Account by Steam Guard, to protect".
- If you log on to a new Computer, you need to specify from now on, in addition, a verification code will be sent to your E-Mail address.

Steam Guard enable
If you have the Steam Guard enabled, you can also collect cards to sell.