To get started, you'll need to get familiar with Repo and Version Control with Git.
# Create a directory for the source files
# You can name this directory however you want, just remember to replace
# WORKSPACE with your directory for the rest of this guide.
# This can be located anywhere (as long as the fs is case-sensitive)
$ mkdir WORKSPACE
$ cd WORKSPACE
# Install Repo in the created directory
# Use a real name/email combination, if you intend to submit patches
$ repo init -u https://github.com/PixelPlusUI/manifest -b ten
# Download the source
$ repo sync -c -j$(nproc --all) --force-sync --no-clone-bundle --no-tags
# Set up environment
$ . build/envsetup.sh
# Choose a target
$ lunch aosp_$device-userdebug
# Build the code
$ mka bacon -jX