I just downloaded Fracture's Prototype Portivity Combo Gun, as found in this thread:

https://forums.thinking.withportals.com/community-releases/the-prototype-portivity-combo-gun-t10700.html

...and I believe also in this map:

https://steamcommunity.com/sharedfiles/filedetails/?id=927805956

I've managed to get some maps for Portal 2 working before, but as this is not a map, I'm at a loss for what to do. I would greatly appreciate a simple tutorial as for what needs to be done for me to use this gun in-game.

As a side-note, this may be a given, but once installed, would it be possible for me to use the gun during the singleplayer campaign(via console commands, ect)?

That download has an included readme inside the 'Energy Ball Import' folder in the zip.

Quote:
Place the following folders into one of the game directories below for energy balls to appear normally,
whichever one you installed the game to.

C:\Program Files (x86)\Steam\SteamApps\common\Portal 2\portal2
C:\Program Files\Steam\SteamApps\common\Portal 2\portal2

You will require pakrat in order to use them on the PTI workshop as well

https://developer.valvesoftware.com/wiki/Pakrat