Score! If you plan on wearing goggles and gloves, gear up now. To score the glass, place the straightedge along the line or marks you made. If the straightedge feels slippery, put a piece of masking tape on the underside to improve its stability.
Dab a drop of cutting oil on the cutter wheel, and place the side of the tool against the straightedge at the far end of the cut line. Pull the tool toward you, using moderate force in one smooth glide.
If you hear a ripping sound, you’ve got the pressure just right; if it sounds like there’s grit on the glass, easy up. Keep going in one single motion until you reach the end. Retracing the score mark increases the likelihood of ragged edges and a bad break.