How Do You Make Addon Packs In GMod

Hello i would like to know how you make add on packs for Gmod i have a server that ahs a pointshop and some players get errors when there looking at stuff so i would like to know how this happends and how to fix it or if someone can do it for me thanks bye

[editline]30th June 2013[/editline]

I have a mac btw