Here's how you snap a piece of drywall:  1. Using a utility knife, score the drywall's front side along the desired cut line.  2. Lay the scored line across an impervious surface, such as the edge of a workbench.  3. Apply even pressure along the scored line to the drywall's backside. 4. To make the appropriate cut, the drywall must snap cleanly along the score line.