EuroOffice Extension Creator development is managed through Launchpad at https://launchpad.net/eoec/. Stable releases are available at https://launchpad.net/eoec/+download and the live source code can be checked out from the Bazaar repository lp:eoec.
Using Bazaar is surprisingly simple. Installation instructions and downloads for every platform are at http://doc.bazaar-vcs.org/latest/en/mini-tutorial/index.html#installation. Once it is installed, just execute
bzr branch lp:eoec
and the latest source code will be downloaded. Now you can edit this source code and make commits, but take note that these commits are only made to your local repository. When you have created something magnificent, you can upload it to Launchpad, and the EuroOffice Extension Creator maintainers can then take a look and accept the changes. This process is slightly more complicated than checking out, but it is well described at https://help.launchpad.net/Code/UploadingABranch.
Now that the source code is on your computer you can start using EuroOffice Extension Creator, so on to the next section!