This handbook explains how to do the common tasks of an Ubuntu package maintainer. In particular, it explains how the git-ubuntu tool-suite is used for working with Ubuntu packages.
If you are interested in contributing to Ubuntu, you may want to attain certain uploading rights. For guidance on where to start, check out the path to upload rights page.
Note that this isn't a policy document; the official policies will be linked to where possible and should be referenced for the officially correct ways to do things. Instead, this is intended to serve as a tutorial style introduction to help new Ubuntu packagers get up to speed.
Similarly, this handbook doesn't attempt to cover topics comprehensively. There are many ways to do things, and some alternate approaches may be faster or better in special cases, but this will try to provide the reader with a solid working knowledge of one robust process for accomplishing work items.