There are several different types of organs, both acoustic and electronic. Here are some examples, starting with the most common.
A reed organ or pump organ is one which is operated by two foot pedals to pump air into bellows. The air is blown across "reeds" inside the organ as keys are depressed in order to create sound. The sound of a reed organ is similar to that of an accordion and uses the same sort of technology. Reed organs can be very basic in design or very elaborate with intricate wood carvings and a decorative hutch. Sometimes the organ will have a second keyboard. See top photo, left.
A spinet organ is a small electronic organ. They were designed for home use and are not suitable for church use due to limited capability and range. They most often have only 13 stick-type foot pedals in addition to one volume pedal and two offset, short keyboards, meant to keep the left hand on the bottom and right hand on the top. These were most popular between about 1950 and 1980. See bottom photo, left.