When you purchase a permanent licence from our website you are entitled to getting Steam key(s) for what you have purchased.
After doing this, you should get a "Add to Steam" button next to your licences.
In GameMaker: Studio and GameMaker Studio 2, clicking on the "Add to Steam" button will automatically add your licence to your Steam account and the next time you log in to Steam it shall appear.
If you have already got certain licences/Modules on Steam then it will show up as "Already owned by <Steam Account>".
Note: Please double check the Steam account linked to your account as this cannot be undone after this point. You will not receive additional Steam keys for anything you already own on the current Steam account.