Clone into phpBB/ext/gallery/core:
git clone https://github.com/nickvergessen/phpbb-ext-gallery.git phpBB/ext/phpbbgallery/core
Go to "ACP" > "Customise" > "Extensions" and enable the "phpBB Gallery Extension" extension.
We use Travis-CI as a continous intergtation server and phpunit for our unit testing. See more information on the phpBB development wiki.
