Protect your eyes with safety glasses and wear long pants and closed-toe shoes. Though relatively safe, edging the grass can cause loose to debris to shoot up unexpectedly.
Move the lawn edger over to one end of asphalt surface where the lawn and asphalt meet. Position the edger so that the rotary string is between the edge of the asphalt and grass turf. The wheels of the edger should remain on the asphalt. Only the rotary string should overhang onto the grass turf.
Turn on the edger and walk it in a straight line down the length of the border. Keep close attention to what you are doing so that you keep the edge straight and that you do not stray too far from the edge of the asphalt and expose more than necessary.
Power off the edger once you reach the end of the asphalt surface and clean up the grass turf clippings and any other debris from the surface.