Some bacteria have one flagellum, some have a few, and some have many - depends upon the bacterial species. The location of the flagellum or flagella can also be distinctive. A single flagellum can extend from each end of the cell - amphitrichous . The flagellum structure is a remarkable thing. The filament is the long part, the hook is a wider region at the base of the filament - where the surface of the cell is located, and the basal body anchors the flagellum to the cell.
Energy generated by the cell is used to cause the flagellum or flagella to rotate.
If there are flagella all around the cell, each flagellum intertwines with the others to form a single filament which extends from one end of the cell - quite amazing. The basal body consists of the filament which at this point has become a more narrow shaft which goes through the cell wall and the plasma membrane underneath, and a series of rings around the shaft. The rings which surround the shaft appear similar to and appear to have the same function as bearings which surround the shaft of any mechanical motor. The rings are static - as is the basal body. No one yet understands how the energy is applied and transferred as a physical force to cause the shaft to rotate.