To get started with Android/ExtinctOS, you'll need to get familiar with Source Control Tools.
To initialize your local repository using the ExtinctOS trees, use a command like this:
repo init -u https://github.com/ExtinctOS/manifest.git -b bka --git-lfs
Or If you wish to save some system space and don't care about repo history depths:
repo init --depth=1 --no-repo-verify --git-lfs -u https://github.com/ExtinctOS/manifest.git -b bka -g default,-mips,-darwin,-notdefault
Then to sync up:
repo sync -c --no-clone-bundle --no-tags --optimized-fetch --prune --force-sync -j$(nproc --all)