It depends on a couple things mostly if you are on that type. A friend of mine just got command, and he first went a team building course, then he flew with special captains and on those flights he played the captain role but flight from the right seat. I can not remember if he had to go to a ground school however I suspect he did, then he went in the sim, after that he flew from the left seat with a captain who played everything from a confident jet jock, to a enthusiastic but helpless new guy, then he took a final check.
If you change aircraft you have the aircraft transition in there too, which is probably a longer ground time, and more sim, and flight training.
>>only on certain aircraft? What qualifications must you possess? <<
Airliners you can only fly one type.