Most weed trimmers are tap and go. You tap the head on the ground to release more line as the line wears down. If the line on the trimmer is not wound properly, your line will get caught or hung up. When this happens frequently, it can turn a 15-minute weed trimming into an hour-long project, so it is best to wind the line correctly in the first place.
Remove bobbin from string-holder casing. This is the center piece on the bottom of your trimmer. Depending on the trimmer model, there may be one or two buttons on either side of the casing that must be depressed in order to remove the head.
Insert trimmer line into hole in the bobbin from the inside, until about a quarter inch is poking through to the outside.
Hold the line in place with your index finger on the outside of the bobbin while you wind the line around the head the first few times, to get it started.
Wind line in the direction indicated by arrow on the bobbin. Wind line evenly, from top to bottom of the bobbin, keeping the line taught. Repeat to make another layer, each time going from top to bottom in even, parallel lines. If lines cross, it will get stuck as you are trimming.
Cut the line with scissors, when enough line has been wound to fill the bobbin just to its outer edge. Do not overfill.
Place end of line through the hole in the string holder casing from the inside, so that it pokes through just enough to reach the metal piece on the guard plate, (about 6 to 8 inches, depending on model). When bobbin head is tapped, the line should release smoothly. You are now ready to trim weeds, hassle free.