Bob is a build automation tool inspired by bitbake and portage. It is intended for complex embedded projects and thus focuses on reproducible builds while still being nice to developers in agile environments.
It's probably the best to head over to the documentation. To get an impression of how Bob is configured, have a look at the tutorials. A real project that is built by Bob can be found here.
If you have a specific question you're welcome to post on the mailing list (FreeLists).