doit documentation introduces the concepts of every feature one by one with examples. It is the preferred way to learn doit and it also serves as a complete reference. You may skip parts of advanced task configuration used on non trivial work-flows on a first read, but make sure you reach the docs describing the command line...
The total reading time for the whole documentation is about one hour.
For a short introduction check the articles below:
- Software Carpentry: Automating an analysis pipeline using doit.
- Create a command line program using doit as a lib: Power up your tools