A single handle or single lever shower valve will have a lever or knob style handle.  The lever or know will pull out to turn on and pushed in to stop the flow of water.  Temperature will be determined by rotating the handle either clock wise or counter clockwise. A two handle shower valve controls hot and cold water through each handle. A three handle shower valve controls both the hot and cold water along with a diverter handle that shifts water flow between the showerhead, other shower attachments, or a tub.
VMS stocks a wide variety of tub and shower handles from lever designs to knob and ball style handles in a selection of materials.