I have used GodotSteam only one time for a quick test, so take my insight with a grain of salt
First of all, are you sure you want to use a module ? To use a module, you have to use an editor+templates compiled with the corresponding module. You can download those under the “Module Pre-Compiles” sub-section, of the “Download It” GodotSteam section.
I find it less restrictive to add an external dependency in Godot via the addons/plugin system. In your case, in Godot 4, you should use the GDExtension plug-in. (In Godot 3, you should use the GDNative plug-in)
Download the GDExtension plug-in matching your engine version (you need 4.2 if you use Godot 4.2 !!!)
Extract the content of the zip file
Add the “addons” folder DIRECTLY into your project root
From there, you should be able to access the GodotSteam API from GDScript, in your project. I can only wish you luck at this point, as I haven’t tried to do what you’re doing !
When you’re sure everything is set up, you can take a look at those tutorials :