Hold the staple gun upside down and locate the black staple loading area. Push up and forward on this area and pop out the staple reservoir. Make sure that there are no staples or debris jammed inside of the reservoir.
Load the staples of your desired size into the gun. The staples should be facing up and should be tightly held together and not broken. You want to place one long, unbroken bar of staples gently into the gun and slide them all the way forward.
Close the staple reservoir securely to lock the staples in. Test the gun once by shooting out a staple to make sure it is firing correctly.