What do some letters and numbers in the score of classical guitar mean?

In classical guitar music, letters and numbers such as P, A, M and I usually indicate the position of fingers on the guitar strings, as follows:

P: Just play the guitar string with the thumb of your right hand.

-m: refers to playing guitar strings with the ring finger of the right hand (wooden tower).

-i: refers to playing guitar strings with the fingers of your right hand.

In addition, the number indicates the specific position on the guitar string. For example, the number 1 is on the first guitar string, the number 2 is on the second guitar string, and so on. The circled numbers indicate the number of strings to be played. For example, the circled number 1 indicates that the first guitar string needs to be played, the circled number 2 indicates that the second guitar string needs to be played, and so on.

These symbols usually appear above or below the notes of the guitar score, indicating which finger should be used to play which string.