You will then enter the Counter-Strike: Global Offensive game page which will look like this.
Add a Steam account
To connect your Steam Account, click on the "Connect Steam" button below the game title.
This window will pop up which will explain the details about our Anti-cheat Policy for CS:GO.
By clicking on the Sign in through Steam button you will be redirected to the Steam account verification page (outside Challengermode).
Simply verify your account there (log in) and you will be redirected back to Challengermode. You'll know when you're done if you can see your Steam account like so:
Please note: If your Privacy Settings on Steam are set to Private, you will not be able to link your Steam account. After making it Public it may take up to 15 minutes until you can link your Steam account to Challengermode.
If you're not certain about the process of making your Steam profile Public, please follw the steps in this article: https://help.challengermode.com/other-faqs/make-your-steam-profile-public