LG Optimus V apps question?

New android phone,still learning, so bare with me please. My apps are constantly running. I have used an app killer but once you open the app killer up again it seems like it always has more apps to kill and usually of the same ones that were just killed. I understand that certain actions while using the phone will cause some applications to start automatically, that's fine. But is there a way to actually stop the apps from starting without you specifically turning them on yourself? Even when I go into settings and "forcefully" turn the app off it still pops back on.

OR is that why with the app killer you have the option to put a timer on the "app killer"? And if so what should the frequency be, every 5 minutes, every hour, etc?

Thanks!