To get started with the PixelOS sources, you'll need to get familiar with Git and Repo.
To initialize your local repository, use command:
repo init -u https://github.com/PixelOS-AOSP/manifest.git -b thirteen
Then sync up:
repo sync
Initialize the ROM environment with the envsetup.sh script.
. build/envsetup.sh
Lunch your device after cloning all device sources if needed.
lunch aosp_devicecodename-buildtype
Start compilation
make bacon