Hmmm...I can't remember even ever looking at the manuals years ago. I think they were just very basic stuff like what leaders, units, civs, etc. are in the game. And in cases of say the expansion, what the new stuff is. The manuals are not going to teach you how to play the game. Anyway, I think most of what you'd find in any manual can be found here at CFC:
http://www.civfanatics.com/civ4/
The Civlopedia and Info Center mainly will get you acclimated to what is called what. War Academy was member generated, but most of the strategies there are rather outdated.
The Strat Article subforum of the S&T forum contains more recent member created content that will be useful, though some can be advanced initially. However, these few in particular may benefit you sooner than later:
Sisuitil's Beginner guide was an old standby for many years to ease newer players into the game at Noble level and below. Definitely one I read initially many years ago. It can be found here:
https://forums.civfanatics.com/threads/sisiutils-strategy-guide-for-beginners.165632/
A little bit of his stuff is slightly outdated, and again, geared toward lower level newb play. Higher difficulties really changes things up a lot. Still it is a good introductory guide that many old folks here used years back.
Know Your Enemy article is a relatively recent guide that translated the code diving a member did many years ago into a more readable tool. Helps understand how the Leader's in the game think so as to improve your diplomacy. It's always a good reference and I often use it if I can't remember how a certain leader deals with certain things. Found here:
https://forums.civfanatics.com/threads/civ-illustrated-1-know-your-enemy.478563/
City Placement guide is a useful tool to understand how to optimize your empire. Created by a good player not long ago. Found here:
https://forums.civfanatics.com/threads/civ-illustrated-2-case-studies-city-placement.546356/
City Specialization is a bit of an advanced, but important, concept, and a discussion of that occurred in this article:
https://forums.civfanatics.com/threads/civ-illustrated-3-city-specialization-explained.547564/
All these guides are BTS focused and in order are gradually more advanced. It will take time to grasp all the concepts so don't feel overwhelmed. Take your time and just focus on little things first and then build off of that with new concepts. The Know Your Enemy (Diplo) reference is not so much concepts anyway and a tool you can always refer to when needed. Quite a few more articles in there that may be useful but probably far advanced for you at this stage.
Lastly, it is indeed good to read up and practice these concepts, but the best way to learn fast is to post a shadow game over in S&T.
