First, check your string supply
Twist off the head of your lawn trimmer to check how much string you have. You may want to replace it if there is very little left. If you have quite a lot of string left, you may still want to take it out and restring it if it has come loose or been damaged.
Choose the right replacement string
You can buy a string that aligns with the type of gardening you are doing. If you are cutting grass and weeds, you do not need anything more than basic weed eater string. If you are cutting tall grass or want to use your weed eater as a substitute for a lawnmower, you should buy a heavier string that will not break in extreme conditions.
Turn off and unplug your weed eater
You should turn and/or unplug the weed eater before you do anything. You should also check the head of the device to make sure it is not hot. If it is, wait a few minutes.
Before you begin, you should remove any grass or lawn debris that is stuck to the device. Grass and lawn clippings will build up on the device, and it could clog while you are working.
Twist off the head of the spool
Most weed trimmers have a head that you twist off to reveal the spool of string. You should read the instructions on the unit to determine which way to turn the head of the device. Twist it off carefully, and you will see the spool of string that remains. The rest of the spool is attached to the weed eater, and it cannot be removed. Keep this in mind when you are removing the cap. If you pull too hard, you might break the part of the spool that is attached to the unit.
Remove any excess string
Excess string will get in the way of any new string, and you cannot add the string properly if you do not pull out the old string first.
Find the hole where the string is installed
You should insert the tip of your string into the hole and start to turn the spool so that the string will wrap around the spool. At this point, you can spin the spool, add as much string as you need, and stop turning the spool when you cannot add any more string to the unit.
Snip the string when you stop
You need to leave about six inches of string hanging from the spool when you are done adding your new string. You should use a heavy-duty pair of scissors to snip the string.
Then replace the cap. Make sure that the cap is locked into place. Once you have done this, you can power up your device and make sure that it works. If the string does not turn or the head is not attached properly, your machine will not run.
If this happens, turn off and unplug the machine. You can remove the cap, check the string, and reinstall the cap properly.
You are now ready to use your weed trimmer around the lawn, and you can show everyone in the house how to put string in a weed eater if they want to handle the lawn duties.