There are many different types of organs but principally there are pipe organs and reed organs.
Pipe organs, as you discovered in the “Bach and the Pipe Organ” CD/MP3, are built into a room. You cannot move them. Reed organs, however, are more the size of an upright piano and can be moved. Other than size and portability, how are they different?
Pipe organs make their sound with wind passing through the pipe and out through the “lips” of the pipe. This is very much like how a flutist make a sound on the flute.
Reed organs make their sound by wind vibrating a reed, very much like an oboe or a bassoon.
Unlike the pipe organ where you have an electric motor pumping air into the bellows, with the reed organ you fill and empty the bellows by moving the pedals up and down with your feet. You must pump the entire time you are playing.
NOTE: It is interesting that the pipe organ pipe calls its opening the “lips” and the reed organ calls the vibrating part the “tongue.”