The focal length lens you want to use will depend on the size of the field you want to capture. A typical 35mm camera and 90-100 mm lens will provide approximately a 30 degree field of view. For some nebulae and star clusters that are only a little more than a degree in angular size, it will be necessary to use a camera lens that is much longer, perhaps approaching the focal length of a typical telescope. Thus, the mount and drive are important, but require less precision than for prime focus photography. This will not be discussed here, but is a good place to start for photography that involves some tracking.
Star trails are the simplest astrophotographs to take.
They require only a stationary mount, such as a tripod. A dark sky will help, but is not absolutely necessary. Just open the shutter and wait a while. It is usually very clear after just a moment's thought why the telescope needs to have a drive for most photography. Another source of error, which is correctable to some extent, is misaligning the mount with the pole.