HelpHeaders and code needed for a C++ hack?

Hey.

I want to make a C++ hack, but I don't know what headers and stuff like that I need. I tried GLua Headers, but I got stuff like how "pLuaShared" wasn't a variable and stuff.

Do I need like Source SDK 2013? If so, what specific files from it?

Thanks

You don't *need* the source sdk, but you can use it. Or you could just make your own little SDK that only has the stuff you need in it, which can be found with a little bit of reversing in olly/ida (or look at someone elses, and test/change it to work on garry's mod).
There are many open source cheats available with just a little bit of searching. I haven't really looked at many of these but https://github.com/skimmilk/skimbot looks like a good source (made for TF2) that you could use as a reference.