Jack
A few starting places:
http://www.photocourse.com/multimedia.htm covers basic concepts
http://www.nikondigitutor.com/eng/d40/index.shtml based around the d40 rather than the d50 but gives a few good videos covering the basics - on the menu on the left hand side I would start with the PSA and M modes
http://www.nikondigitutor.com/eng/d50/index.shtml is the d50 equivalent but I've not looked at this one before.
Have fun
James
DCM GalleryThe Best Photographer in the World 3 times