It sounds like the letters are labels showing the vertices (corners) of the shape. Each vertex is a point whether it’s a dot on the shape or not. But I would have to see the actual picture of the shape to tell you what the dots mean, because the dots might be used for a different purpose.
Line segments, for example, have two endpoints, and these are often represented by dots. This means that the line represents all the points between and including the endpoints. If a dot is missing, the endpoint itself is not included. Sometimes a tiny circle is used to show that the endpoint is not part of the line.