Before beginning your slab pot, you will want to create a thick slurry. (Allow some scraps of clay to dry completely over several days, then drop them into a container with just enough water to cover them. They will quickly dissolve to create a slurry.) By using slurry instead of water, you increase the joint's strength, both in the building process and throughout the pot's life.
For small pots, you can press out slabs. Compress a lump of clay into a ball about 2 inches in diameter. Using your palms, flatten the ball as much and as evenly as possible.
Place the clay pancake on a canvas-covered work surface. Continue flattening it by pressing it against the work surface with your palm or by pounding on it. The final clay pancake should be of an even thickness, of about 1/4 to 1/2 inch. Carefully lift the slab, releasing it from your work surface.
For a larger pot, you can roll out slabs using a rolling pin.