Dodging makes areas of a print lighter, and burning makes them darker. Dodging is typically done with a circle of card attached to the end of a piece of wire. While you're exposing the photographic paper under the enlarger, you basically just waggle it around, casting a shadow over the area you want to lighten. Conversely, burning is done with a piece of card with a hole in it, where you block off most or all of the light except for the area you want to give more time to and thereby make darker (the paper produces a negative image). It's quite tricky and takes a lot of practice. The dodge & burn tools in Photoshop are *much* easier to use!