How do to tension and true a rear wheel with a warped rim?
You need a good book, and, unfortunately, no really good books on bike maintenance have been written in about 20 years.

Two that you might be able to buy used are:

Effective Cycling
By John Forester
MIT Press, 1984

The All New Complete Book of Bicycling
By Eugene A. Sloane
Simon &amp; Schuster, 1980


Both contain decent discussions of wheel building and truing.