To get started with Android/UBPorts, you'll need to get familiar with Repo and Version Control with Git.
To initialize your local repository using the LineageOS trees, use a command like this:
repo init -u https://github.com/Martini-Lab/android.git -b ubports-9
Then to sync up:
repo sync --force-sync --no-tags --no-clone-bundle -j$(nproc --all)