Cake- These tobaccos are cut tobaccos that have been put under pressure, and are normally sold in slices. The usual way to ready them for the pipe is to break up the slices in your hand. The main thing to consider is how small you want the pieces to be. Breaking the tobacco up finer will give you more flavor, but it will burn hotter. Larger chunks will release less taste, but the tobacco will burn slower and cooler.
Flake- Similar to a cake, but pressed from large leaf, and usually sliced a bit thinner. Many people prefer to just bend a few flakes and stuff them in the bowl, topping it with some fine pieces to get it lit easier. This will result in a cool smoke, but may require more maintenance while smoking. They may also be prepared the same as a cake (above).
Spun cut- These tobaccos come in the form of coin-shaped pieces. Prepare them the same as a flake- stuff the whole coins in while topping it with finer pieces, or rub them out fine and pack as normal.