I originally learned celestial navigation from a text book that I picked up at a second hand store. It was designed to work with a standard set of step by step forms. It was a time consuming process to reduce a sight. Today there are easier methods and specially designed calculators that make reducing a sight much easier and there seems to be reasonably clearly written texts out there. I looked at one at Barnes and Noble not that long ago.
There also are schools and videos on the subject. School of Ocean Sailing offers live-aboard celestial navigation courses. www.sailingschool.com
You can download a short guide to Celesial Navigation at: http://home.t-online.de/home/h.umland/page2.htm
Some local Power Squadrons will periodically run a celestial navigation course.
One thing I found with Celestial Navigation is that it is strictly use it of loose it. I have not done anything with celectial navigation in over 20 years and doubt that I could take a good sight or reduce a sight without a lot of struggling.