I'm new too, but I know the basics.
First, you need a dll injector.
I use Extreme Injector v3
http://www.mpgh.net/forum/292-combat...or-v3-3-a.html
Next, you need a dll.
I use Alexander.
http://www.mpgh.net/forum/713-garrys...-bypasser.html
After you get the injector running, click add dll
Add the Alexander dll.
Under Process name, put it, 'hl2.exe'
Now you have your injector and dll working
Now you need an aimbot
I recommend AHack or hera
http://www.mpgh.net/forum/713-garrys...-v1-0-0-a.html
Download the file, then put it under
C:\Program Files (x86)\Steam\SteamApps\common\GarrysMod\garrysmod\l ua
You're now good to go!
After that, join a server.
Hit the 'Inject' button on Extreme injector.
Then, in console type 'lua_openscript_cl 'filename.lua'
Replace 'filename' with what you name AHack.
Mine is named ttt3
After that, type 'Ahack_menu' into console
Have fun!