The ladder hop is a simple exercise you can do to improve quickness on your feet. In order for this drill to be effective, it must be performed with speed and precision. The "two in two out" reference means that both feet will enter a ladder square and both feet will jump outside of a square. Here are the instructions:

First, jump in the first square with both feet. Jump again to the outside of the second square. Repeat the sequence on the remaining squares. Be sure to stay on your toes at all times.