The following chart shows how to produce individual notes on the guitar:
The strings are named 1-2-3-etc from the highest pitch (1st) to the lowest pitch (6th).
There are several possible tunings for strings, but the picture above shows the standard tuning.
When the strings are plucked individually (with the right hand, leaving the left hand off the neck), in the standard tuning, they produce the following notes:
To produce different notes, press a string on one of the frets with the left hand, and pluck it with the right hand.
For example, as shown on the figure above, the first string pressed on the first fret, produces an "F" note; the same string on the third fret, produces a "G" note, etc.
The following alternative chart shows the notes produced by each string, when pressed on each fret: