Cat II / III
The procedure for landing in Cat II or Cat III will be given in the Flight Crew Operating manuals.
Whether it is possible to fly such an appraoch manually or only on AutoPilot, depends on the aircraft type and equipment.
Some aircraft may have equipment, such as a Head Up Display with flare guidance, that make it possible to do the landing manually, even in bad visibility.
Some aircraft may fly so slowly that a manual landing may be possible in Cat II conditions, this might apply to some turboprop aircraft.
However, the usual way that aircraft builders have made Cat II / III operations possible, is through multiple AutoPilots that fly the approach all the way to an automatic landing.