You can read all you need to know and a lot more at http://www.astropix.com/HTML/I_ASTROP/TOC_AP.HTM
Think of the telescope as a prime lens that is manual focus with a fixed aperture. How you use it depends on what you're photographing. An adapter allows the camera to fit where an eyepiece would normally go. Yes, you zoom in by adding more lenses. For telescopes you can use Barlow lenses (designed to magnify eyepieces). Camera teleconverters work too, but the camera doesn't like the absence of a lens so you have to work around that. The more magnification you add the dimmer the image gets, so it only works for small bright targets (Jupiter and Saturn). For small dimmer targets you need more aperture. A lot of planet images start off as video, then the best frames are selected and averaged together.
For faint targets (galaxies and nebulae) you have to do long exposures. You need a mount that tracks the apparent movement accurately. This only happens when it is properly aligned parallel to the earth's axis. The longer the exposure and the longer the focal length the more accurate the mount and the alignment has to be. This is where the added weight of the camera comes in... it can be a problem if you are operating near the limit of the mount.
Anyway, the link I gave describes the sorts of things you can do with different equipment... you can do quite a lot with just a fixed tripod. There are also man made targets up there too, such as the international space station flying past and Iridium flares.
Hope that helps,