Custom gamemode does not show up in dropdown menue

[Obi-Trev]

i am writing this post b/c myself and others are having issues with the first time coding aspect of gamemodes. I have made a custom gamemode, and I believe i folled everything to the Key, but when I load up Gmod, it does not appear in the select gamemode dropdown menue. Is their a distinct source code I need to initiate gmod to load it, or is teir a console command to run it?