How can I fix a guitar string that has broken or come loose?

To fix a broken or loose guitar string, you can replace it with a new string of the same gauge and type. First, remove the broken string by unwinding it from the tuning peg and bridge. Then, insert the new string through the bridge and wind it around the tuning peg, making sure to tighten it to the correct pitch. Finally, trim any excess string length and tune the string to match the other strings on the guitar.