There are three source of help for Timewarrior:
$ man clog
The recommendation is that you go to the Online Documentation and read all of it, in order. This will give you the most thorough explanation of what Clog does.
The online documentation will likely always be more complete and correct, and will be updated between releases.
When you become more familiar with Clog, you will probably refer to the man page or built-in help, which is a more concise reference.