When running your GMOD server, you need to decide who. If these don't work simply just ask in chat if they use pointshop or how to get a different playermodel. GMOD (short for Garry’s Mod) is a Half-Life 2 modification where you can create videos, pictures and manipulate various in-game objects. Most TTT servers will have a pointshop where you can buy different player models/skins with points you receive for playing the server.