The black dots show you where to place your left hand fingers. The white number tells you which finger to place on the string just before the fret. If there is no dot on a string, you play it as an open (not fretted) string.
Other chord diagram symbols that will appear in this book are summarized with the following two chord shapes.
A dotted string indicates that string is not to be strummed. A small bar connecting two black dots indicates they are held down by the same finger. This is called barring.
An X on the string indicates that string is to dampened by another finger lightly touching it. The string is still strummed as a part of the chord but it is not heard.