The game is pretty much straight forward - protect the shielded artifact for 15 minutes.
Kills will make your laser gun more powerful. Gold will unlock some special one time use weapons. Beware shield health is twice bigger than the artifact! You win if you withstand 100% time.
Use this tracker image: https://drive.google.com/open?id=0BygvzTqnzm_weVA5cHByVzNoLTg