If you do obtain the game, these official community guides can help you get started:
When a rival group threatened to monetize parts of the server—locking favorite maps behind paywalls—Riley helped organize a midnight build-a-thon. Dozens of players stayed up, coding and mapping and sharing snacks over voice chat. By dawn, Gmodville had a new central square, built from community art and guarded by a towering statue of a smiling modder holding a soldering iron. Free Steam Accounts With Gmod
Some "tutorials" claim you can get a code after installing apps or completing surveys. These are typically "grifts" designed to generate ad revenue for the scammer while providing no working game key. How to Get GMod Legally (Low Cost or Free) If you do obtain the game, these official