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