1. The string is too low. If the string is too low, it will vibrate against the frets and cause a buzzing sound. To fix this, you can raise the string by turning the tuning peg clockwise until the string is high enough to clear the frets without buzzing.
2. The nut is too low. The nut is a small piece of plastic or bone that holds the strings in place at the headstock. If the nut is too low, the strings will not be held in place properly and will vibrate against the frets, causing a buzzing sound. To fix this, you can raise the nut by adding a shim (a thin piece of material) underneath it.
3. The bridge is too low. The bridge is the part of the guitar that holds the strings in place at the body. If the bridge is too low, the strings will not be held in place properly and will vibrate against the saddle (the small piece of metal that the strings rest on at the bridge), causing a buzzing sound. To fix this, you can raise the bridge by turning the screws on the bridge posts clockwise until the strings are high enough to clear the bridge without buzzing.
4. The frets are worn. If the frets are worn, they will not be able to hold the strings in place properly, causing them to vibrate against the frets and create a buzzing sound. To fix this, you can have the frets replaced by a qualified guitar technician.
If you have tried all of these solutions and your guitar is still buzzing, you may need to take it to a qualified guitar technician for further diagnosis and repair.