The main Bubble view shows a pyramid view of all the people in your downline and what their position is by the color of their bubble. The numbers shown on a person's bubble indicates how many people are listed below them. Bubbles with the envelope icon indicate people who have been invited to the Bubblr, but haven't logged on yet.
You can also choose to display a radial version of the bubble view of the people in your downline showing their position by the color of their bubble.