To get started with FlexOS, you'll need to get familiar with Git and Repo.
To initialize your local repository using the FlexOS trees, use a command like this:
repo init -u git://github.com/FlexOS/manifest.git -b lp5.1
Then to sync up:
repo sync
To build FlexOS
$ cd ~/flex
$ . build/envsetup.sh && brunch <device>