To get started with Android/LineageOS, you'll need to get familiar with Source Control Tools.
To initialize your local repository using the LineageOS trees, use a command like this:
repo init -u https://github.com/brbtrt/EOSP_android -b lineage-19.1
Then to sync up:
repo sync
Please see the LineageOS Wiki for building instructions, by device.
All supported devices are built weekly and periodically as changes are committed to ensure the source trees remain buildable.
You can view the current build statuses at LineageOS Buildkite.
Builds produced weekly by the buildbot can be downloaded from LineageOS downloads.