A pyramid of numbers is where the size of the box represents how many of each type of animal there are in a set area. For example, in 1km of African grassland, there may be millions of grass, 2-300 buffalos and 1 leopard. On these, the lowest box would be the grass, the second box up the buffalos and the top box the leopard. Each of these levels is a trophic level.
A pyramid of biomass is a pyramid where the boxes represent how big the organisms are in weight. These are often better when an extremely large plant or animal is involved, for example a tree.
A pyramid of energy is where the box size represents the amount of energy in an organism.