After downloading the mod, use a program such as 7zip or WinRAR to extract the main folder of the mod.
Navigate to assets/mod_overrides. The assets folder is supposed to be in your game's installation folder (don't know where that is? click here). Create the folder if necessary
Move the main folder of the mod from step 1 to the folder you navigated to in step 2.
Follow instructions here also!
Choose if you would like the complete pack or choose your own sounds
2. If you choose the entire pack listed in files as "csgo sound pack complete" just put the whole folder in mod_overrides
3. If you choose to pick you own listed in files as "csgo sound pack individual" you will have to drag individual guns (for example if you want the deagle only drag and drop "csgo deagle (deagle)" folder from the pistol folder into mod_overrides, if you put the whole pistol folder it will not work)