You may want to look over the Laser Lenses, Optics, and Focus article before performing this test. It’s a good primer on optics.
The ramp test is a method for determining the optimum focal distance between your focusing lens and the material you’re cutting. You can place a block of wood that has been cut at an angle (the ramp) on the bed then engrave a straight line up the ramp. The point where the burn size is the smallest is the focal point for your laser.
Generally speaking, when engraving you will want the surface of the material to be at that height and when cutting you will usually want the center of the material to be at that height.