To get started with Android/LineageOS, 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/lineage-OS-MOD/android.git -b lineage-17.1
Then to sync up:
repo sync --current-branch --force-sync --no-clone-bundle --no-tags --optimized-fetch --prune -jx
Please see the LineageOS Wiki for building instructions, by device.
source build/envsetup.sh
lunch lineage_device-userdebug
mka bacon