Set up the movie projector so it's projecting onto a white wall (or, better yet, an actual movie screen) and thread the desired movie into it.
Using a tripod for steadiness, place the VHS/digital camcorder as close to projector as possible, pointing it toward the wall/screen.
Turn the projector light on only, and frame the VHS/digital camcorder so that the bright, white, 4:3 rectangle fills the camcorder frame.
Run film through the projector and adjust the focus on the camcorder accordingly. (Most camcorders have an auto-focus feature.)
Once the focus on the camcorder is set (whether manually or automatically), back the film up and press "Record" on the camcorder. The film's image should fill the camcorder frame fully, and the 8mm film is now being recorded onto VHS or digital video.