Lay the glass on a flat surface, such as a dining room table or a work bench.
Measure the size of the glass that you need to cut using a tape measure and mark the glass with a dry erase pen.
Align the straight edge along the marks made by the dry erase pen.
Hold the straight edge firmly in place with one hand while holding the glass cutter in the other hand. Press the cutting wheel to the glass and apply steady even pressure as you cut along the marked line. This will create a small fracture in the glass.
Hold the glass over the edge of your flat surface and tap with the blunt end of the glass cutter along the cut line. This will separate the fracture and create two pieces.