There are two ways to MIG weld. The first and the most common is to push the MIG gun toward the direction of the weld, this is called forehand method. Forehand welding produces shallow penetration with a flat wide smooth surface. The second is backhand method where you drag the MIG gun like a stick welder. This produces a deep penetration weld that is narrow and is high in the center. In most cases you will be forehand welding and it is very rare to do backhand welding.