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