The clay gun, or "extruder", as it is also called, works like a cookie press. Fill the cylinder with your choice of clay, choose a disk, and push the clay through the openings in the disk. The disk design determines the shape of the clay as it leaves the extruder. Disk designs range from basic geometric shapes (various sizes and numbers of circles, squares, and triangles) to highly specific shapes such as hearts, teardrops, and pumpkins.
Traditional extruders can be rather hard on the hands and difficult to work (with the exception of only the very softest clay), but there are special extruders that are less painful to operate. It is also possible to adapt traditional extruders with a caulking gun or wood bellows (two hinged 2x4s and a couple of strategically placed holes) to increase the leverage.