This module is used to make a NixOS system capable of gaming.
This module when loaded changes the settings in such a way that the system should be capable of gaming. It also installs Steam.
This is what the options look like you can add to your machine-settings:
{
machine-settings.system.modules.gaming = {
enable = boolean;
};
}
Take a look at this article on the NixOS wiki about Steam for more information.