Installation Guide:

(Make sure its in your mods folder.)
Simply extract the files from the archive and place them into any .rpf archive from a recent update.
Alternatively, you can opt for adding modded weapons into an addon DLC.

FiveM Installation Guide:

Create a folder inside your FiveM Server as a Directory named "l115a3" or whatever you choose

Drag the "fxmanifest.lua" & "stream" folder into your created folder or the one provided.

Go into your servers "server.cfg" and type "start [resource name]"