To get started with Android, you'll need to get familiar with [Git and Repo] (http://source.android.com/download/using-repo).
To initialize your local repository using the aospX trees, use a command like this:
repo init -u git://github.com/aospX/android.git -b ics-devel
To build a snapshot release, use a command like this:
repo init -u git://github.com/aospX/android.git -b ics-devel -m MSM7230BR20603.xml
Then to sync up:
repo sync
To build:
. build/envsetup.sh
lunch aospx_ace-userdebug
make -j4 aospx