What are the letters and numbers written above guitar music?

The letters and numbers written above guitar music are called tabs. Tabs are a simplified form of musical notation that shows which frets to play on the guitar. Each string is represented by a number, and the numbers indicate which fret to play on that string. For example, if you see the number "3" written above the third string, it means to play the third fret on the third string.

Tabs are often used for teaching guitar because they are easier to read than traditional sheet music. However, tabs only show which frets to play, and they do not provide any information about rhythm or timing. So it is important to listen to recordings of the music as well as read the tabs in order to learn how to play a song.