The Olympic Rings are composed of five rings. There are three at the top - one blue, one black and one red. There are then a further two below this - one yellow and one green. The rings are all intertwined with each other. See the related link for an image of the Olympic Rings.
Actually I think the rings are more important in promoting the Olympic games than at the games themselves, but the five interlocking rings represent the union of the five main regions of the world by the meeting of their athletes.