The VRCFury setup is relatively simple

Scene Setup

Find the FlareGun Prefab in the ‘INSERT FOLDER PATH HERE’ folder and drag it onto your avatar so that it becomes a child object of the avatar.

If you need to scale the system only scale the Parent FlareGun System Gameobject. Try not to scale any of the gameobjects inside the prefab as that may result in undefined behavior.

Setting up the Hand Offsets

Find the Left and RightHand Offset Targets. You’ll need to move these so that the Red and Blue placeholder objects inside of them are lined up with your avatar’s hands in the way you want.

DO NOT move the placeholder objects themselves as they do not move the actual location the objects they are representing will be at.

Setting up the Holster Locations

Position the Holster Target where you want the holster to be.

The Holster for the flare gun is initially parented to the hip bone. If you want to change which bone you want to parent the holster to you’ll need to unpack the FlareGun System prefab then select the Holster Target object. On the Holster Target object you can find a VRCFury Armature Link component. Select which bone you want to parent the Holster to from the dropdown

Repeat for the Flare Holster Target.

You do not need to delete the red and blue placeholder objects. They are set up so they will not be included when the avatar is built.

That is all that is needed for the VRCFury setup of the FlareGun. You should be able to upload the avatar and use it in-game.