I have written a fairly comprehensive manual for using Joomla. It doesn't cover templating (making a custom design), or installation, but it's pretty good for learning the back end.
For installation and a lot of other information, check out:
For an excellent tutorial on learning how to create an original template in Joomla 1.5, see:
I hope you find it useful! Let me know if you have any questions.
Download the manual: