The code is hosted on Launchpad. You can branch the latest code from there, and you can also push your own changes as a new branch that can be shared with others. The bzr revision control system is used, at least version 1.12 is recommented (old versions are not compatible with the repository format used on the Launchpad MariaDB trees).
Building the code from source is done with standard Unix tools: CMake (or autotols for MariaDB versions below 5.5), Gnu Make, GCC (or other C/C++ compiler on some systems). On Windows, CMake and Visual Studio are used.
The current state of the source with respect to build/test failures can be seen in buildbot.
For project management and bug tracking, we use JIRA.
The source page has links to instructions on setting up a full development environment, if you are interested.