The chord diagrams on this website contain a lot of information that can easily be confusing. Here's how to read them.
Table of contents
X means that the corresponding string should not be played. O means that the corresponding string should be played without fretting the string (playing the open string).
The low E string is on the left and the high E string is on the right.
The number in the circle indicates which finger you should use to fret a string. The image below shows which finger corresponds to which number.
The letter below a string indicates which note is currently fretted.
The numbers in brackets indicate the interval that is currently fretted. The interval is the distance between the root note of a chord and the current note, but more on this in the introduction to intervals.
In contrast to the diagram on the left, the diagram on the right does not show a specific chord but a chord shape. The shape needs to be moved around the neck to get a specific chord.