If you've just bought a staple gun and have never used one before, figuring out how to load staples into the staple gun can be quite a mystery. It is actually very simple to do once you have located the mechanism that opens the staple loading area.
Locate the release button. On newer staple guns it is a rubber area with grips.
Squeeze and pull the release button.
Turn the staple gun over and place the staples in the crevasse up-side-down, as shown in the illustration.
Make sure that the staples are all level and that none are sticking up above the staple gun.
Push the release button back into place until you hear a click. The gun is now ready to staple.