While this is not difficult to do, it can be slightly tricky. If you follow the steps in the MOGA instruction manual then you're likely to wind up confused because their instructions won't actually work for your purposes.
What MOGA tells you to do is download their app, switch the controller to 'A' mode, and then connect to it via Bluetooth. This will make the controller work with their apps only.
In order to make the controller work with Gear VR apps (or anything non-MOGA), you need to move that switch to 'B' mode. Once you have done this, go into your Bluetooth settings, press 'scan,' and connect to MOGA Pro 2 HID.
To reiterate... being connected to MOGA Pro 2 via your Bluetooth settings DOES NOT WORK. If you are connected to this device it means you are connected to 'A' mode, which works with MOGA apps only.
Connect to MOGA PRO 2 HID instead. This means you can use the controller to play your Gear VR games. The switch on the bottom of your controller must be set to 'B' in order for this to work.
Also, I found that switching the controller to 'A' mode will automatically make the controller show up under 'available devices' in your Bluetooth settings, but when it's set to 'B' mode, you actually have to click 'scan for devices' first.
That's all there is to it. Leave a comment below if you have any questions or still need any help getting your controller working.
Don't have a MOGA controller yet? You can pick one up here.
Want to know more about the MOGA Controller and Gear VR? Click here for my review on both: VR Is Primitive as Heck... and Still Rocks.