DFHack is a Dwarf Fortress memory access library, distributed with scripts and plugins implementing a wide variety of useful functions and tools.
The full documentation is available online here.
It is also accessible via the README.html page in the DFHack distribution or as raw text in the ./docs folder.
If you're an end-user, modder, or interested in contributing to DFHack -
go read those docs.
If the docs are unclear or you need more help, please check out our support page for ways to contact the DFHack developers.