The pencils are so you can loop a rubber band around one side, then stretch the band over your arm to loop on the other side. This is what secures the device to your arm.
You need to post a full tutorial not one where you speed through it all do it in real time where we can actually see each step and the process to complete it
By sliding the projectile through the hole in the front of the barrel, and holding it in place with the block at the front of the lever. You can see this in action at 0:40 seconds
@@BenRebuilt I broke mine with the case on without even moving it! It because I put an electromagnet next to it while it was on and it bassicallly emp my phone