If you are connecting to "large" reflectors or Schmidt-Cassegrain telescopes like a Celestron you use what is called a "T-ring"...it's a ring that screws on to the visual back of the telescope and has the F-mount on the other side. You then attach the camera directly to the back of the telescope like you would any other lens.
For smaller refracting telscopes (the long skinny ones) you need to have an eye-piece projection set up...the set up the telescope normally and a tube holds the camera the correct distance from the eyepiece. You can also use eye-piece projection on the reflectors...but I prefer the direct mount myself.
I haven't had a chance to put my D70 on my Celestron C-8 yet.
Take a look at the How to section of Sky and Telescope magazine:
There are several articles on astrophotography with just a camera and regular lens as well as with a telescope.