Light travels more slowly in glass than in air, so a ray entering the glass bends toward the normal. How much it bends is set by the refractive index through Snell's law: the refractive index times the sine of the angle is the same on both sides. Angles are measured from the normal, the dashed line at right angles to the surface. For this glass the refractive index is 1.5. Use the protractor to set the angle inside the glass to the target, and watch the light flow and bend.