you need to run the emulator you just built. if you've followed the build instructions, it should be on your path, so just run it.
running "source build/envsetup.sh" from the root of your source tree is a good way to ensure you've got pretty much the same setup that google engineers use.
a quick web search found this, which looks about right to me:
http://devtcg.blogspot.com/2009/03/building-running-and-debugging-android.html
(though i'd use "lunch generic-eng" rather than a numeric lunch. and, yes, that really is "lunch", as in "lunch combo", as in "what would you like today?".)
if you want to test on a device, there are extra instructions:
http://source.android.com/documentation/building-for-dream