In its most basic form, digiscoping is a means of successfully connecting a camera with either a telescope, spotting scope, or even binoculars. There are even attachments that allow a person to attach a smartphone camera such as the iPhone to a spotting scope. Often times this arrangement can get you into wildlife photography less expensively than with a DSLR.
At RCS Optics, we recommend getting a 400mm zoom lens for your DSLR. Anything smaller will really limit the opportunities that you will have in capturing some awesome shots.
Alternately, consider the Zeiss photo lens adapter (available with either a 49mm, 52mm, or 58mm thread) that will allow you to connect your DSLR camera to the Gavia spotting scope to offer you an awesome telephoto lens for your digiscoping hobby.
Whatever the arrangement that you come up with, be sure that you have a very stable connection between the camera and the scope, but just as critical is a stable tripod to support your gear. This is particularly important if you are simply holding your camera lens up to the eyepiece of the spotting scope. This arrangement is certainly the simplest, however by taking it a step further you reduce the risk and clumsiness of trying to handle several expensive components simultaneously.
The video below from David Chandler gives a great opening into the use of a Zeiss Gavia spotting scope for your birding or nature observation activities and particularly the range of adapters available for digiscoping as well as astronomical observations.