Guides
The questions on this site tell you what the answers are. These guides tell you how the test around them works: what the officer does, how many questions you get, what to study first, and which rules change depending on your age and how long you have been a permanent resident.
The numbers behind the process
Two data pages come from official statistics rather than from the test: naturalization statistics, from the Department of Homeland Security yearbook, and the N-400 field office table, with the applications each USCIS office received, decided and still has pending.
Then practice
Reading about the test is the short part. When you want to find out what you actually know, take the practice test or work through the 128 official questions, each one with an explanation of why the answer is what it is.
CivicsWise is an independent study site, and these guides describe the rules that USCIS publishes. Each one links the official page it comes from, so you can check any line of it yourself.