When you first log into Challengermode you can find all the available games in the Menu located on the left side, the games you have a account connected for will be in Your Games - any game you still need to connect an account for will be under Other Games.
To add a Steam Account for CS:GO you can do one of two things.
Either hover your mouse over the game CS:GO in the menu to the left, three dots will appear (...) - click these to open up a sub-menu.
In this menu you will find Connect Steam in the bottom, click here to add a CS:SO Steam Account.
You can also click the game name, CS:GO, in the menu - this will redirect you to the CS:GO game page which will look as on the example image below.
You can find the button below the game title on this page, it has the same function as the earlier mentioned Connect Steam button.
This window will then 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 on this page (log in) and you will be redirected back to Challengermode. You will know when you are done if you can see your Steam account on the CS:GO Overview page as on the image below.
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 follow the steps in this article.