To get started with Android/LMODroid, you'll need to get familiar with Repo and Version Control with Git.
To initialize your local repository using the LMODroid trees, use a command like this:
repo init -u https://git.libremobileos.com/LMODroid/manifest.git -b eleven
Then to sync up:
repo sync
Please see the LibreMobileOS Wiki for building instructions, by device.