Warning: use welding gloves and a welding helmet since the brightness can affect your vision and the heat can burn you.

Hold both posts together, and use the weld gun by pressing on the trigger it has while moving the tip of the welding gun from one side to the other. Make slow passes of about 4 seconds between both metal posts since the posts are usually thin.

The welding pattern I used was just move the weld gun's point from one side to the other in a straight line since it is a really small area you are working on.