The wiki contains further general information and documentation about the project. Anything missing below should (in theory) be available there.
Your distribution should provide the latest packages (see the current non-exhaustive list of dpkg downstreams). Otherwise you can get the latest released tarballs for all the supported branches. For historic releases use the Debian snapshot tarballs site, or the historic tarballs used for the VCS switch.
The code under development can be cloned from git, the list of repositories to browse and the instructions on how to clone them can be found in the main cgit interface. There are alternative mirrors at salsa.