Mouse Movement Of Gnome Arm: Sue Blackman's Unity for Beginners

Hey Guys, I am new to Unity trying to teach myself some basics. If you are familiar with Sue Blackman's Unity for beginners, one project is operating a Garden gnome and using the mouse so it controls the gnomes bazooka arm. Using the first person control it has been easy to control the gnome with WASD, but I can't figure out operating the arm.

these are the relevant instructions I followed 6. Drag the Bazooka Arm object onto the Arm Group (First Person Character), and agree to losing the prefab. 7. Drag the GardenGnome onto the First Person Controller. In order for the Arm group to inherit the extra bouncing movement from the Gnome object, you will have to move the Arm Group into the Gnome group. Gnome Motion Root only moves the character around the scene, and it is currently bypassed by Mecanim. 8. In the Hierarchy view, drag the Arm Group onto the Gnome object

this is my first ever post so I apologize if the format is not fantastic. Thanks!