Position an empty plastic tub on the working surface or the ground. If you're using a dry sift screen for sifting dirt, you might set the plastic tub in the garden. The plastic tub must be large enough to catch the quantity of the dry material being sifted. For this reason, use a tub that's the same length and width as the screen.
Place the sift screen on top of the plastic tub. Pile the dry contents over the screen. Gently shake the sift screen back and forth to rock the dry contents. As you sift the contents, the finer dry pieces will fall through the screen and the larger pieces will stay above the screen.
Continue sifting the screen back and forth until all of the material is sifted, then do a second round of sifting if you want to. For a second round, discard the larger materials that are left on top of the sift screen. Remove the tub containing the finer particles and put a second empty tub in its place. Pour the contents from the first tub on top of the sift screen and sift the contents into the new tub.