Start the engine of your grass trimmer. Hold the upper handle with one hand and squeeze the trigger to keep your trimmer running. Hold the assisting handle, in the middle of the shaft, with the other hand.
Hold the head of the trimmer almost parallel with the ground. Lower the trimmer down until the tip of the string is cutting the grass at your desired height. Move the trimmer from the right to the left over the grass to cut it.
Tap the trimmer head on the ground to advance the trimming string. Continue moving over your lawn, holding the trimmer level and steady, until your entire lawn has been cut.
Turn the trimmer so that the head is perpendicular with the ground. Lower the trimmer until the string touches the ground. Work the string down the entire length of the edge of the sidewalk, on both sides.
Release the trigger to stop your grass trimmer.