Take a read through the rulesheet
http://www.ipdb.org/rulesheets/2357/sttng.htm
The game is pretty much built around the missions (modes), you need to do well in those and try to earn the artifact from each one. Then once you've got all the missions done, you can start the Final Frontier 6 ball multi ball where the shot value depends on how many artifacts you picked up on the way.
There is other stuff going on though, read the rulesheet it's pretty thorough