Incandescent lamps work differently. Most of the electricity they use heats a tungsten filament until it glows white hot. As a result, incandescent lamps generate far more heat than a fluorescent light. Since the light source is a single point, incandescents also project light further than compact fluorescents that project a more diffuse light. You should consider this when replacing incandescents with CFL's in high ceiling applications.
Some compact fluorescents have the tubes and ballast permanently connected.
Other compact fluorescents have separate tubes and ballasts. This allows you to change the tubes without changing the ballast. Most lamps consist of parallel, interconnected glass tubes mounted on a base that contains the ballast. The four and six tube lamps keep the overall lamp length short, while providing more light. There are also types that are encapsulated in a glass globe.