To get started with Android/LineageOS, you'll need to get familiar with Git and Repo.
To initialize your local repository using the LineageOS trees, use a command like this:
repo init -u git://github.com/AOSGP/android.git -b cm-14.1
Then to sync up:
repo sync
Please see the LineageOS Wiki for building instructions.
For more information on this Github Organization and how it is structured, please read the wiki article