We're purposely cutting off this user guide at this shallow level of detail. The best thing to read next is the DomTool/Examples, which should introduce by example all of the language features and configuration directives that you're likely to use. If you want to understand the type error messages that the interpreter generates as more than just "there is a problem somewhere," then you'll probably want to learn a bit more about the language.
For a more in-depth understanding of DomTool, including how to build and use your own directives, see the DomTool/LanguageReference. The standard library reference presents all of the standard directives with full DomTool type information. We've glossed over details of the type system in this guide, but members comfortable with ML or Haskell programming will probably find this formal documentation the easiest to use, since types express very succinctly how directives may be used.
The main DomTool page links to all of these resources and several more.