To be honest with you - go pick up a book or an instructional DVD. That's going to be the best way to learn other than simply trial ane error. I've had my D40 for almost 2 months now and I'm just starting to figure things out. There's plenty of good sites out there with quality camera/photography info on them as well. Check out http://www.nikonians.org/for good info on using your D50.

I picked up a copy of this book, and it's been a decent enough starting point for me.

http://www.amazon.com/Digital-SLR-Cameras-Photography-Dummies/dp/0764598031

Good luck!