https://wiki.darkrp.com/index.php/Main_Page
Specificallyhttps://wiki.darkrp.com/index.php/DarkRP:CustomShipmentFields for your gun dealer problem
Also I'd recommend taking a look at the Gmod wiki and looking at code examples to help you with any Lua problems you may have
https://wiki.garrysmod.com/page/Main_Page
If you're STILL having trouble after all that, there are DarkRP & Gmod coding discords out there that you can join and I'm sure that there'll be people there that can help ya
