When are apps realy closed?

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http://forum.xda-developers.com – Hi guys I recently switched to android, now i'm on Panandroid 2.57 Normaly i reach the end of the day with about 40%, but now it gave me a 14% warning at 3 pm (15:00) (btw, after 15 minutes of plants vs zombies it was at 4%, is this normal?) I want to know what states an app can be in. When is an drawing cpu and ram and when isn't it? When i press home, it goes into backgroud, is it just fully operational? Is it drawing power? And when i lock the screen, it is also drawing power? And wen i long-press the home key, and swipe the programms "away", will they be closed now? (HowTos)