Need some info about YOUTUBE

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Here are some of my questions. (1) When i upload a video : a message appears saying that:: Submit this video for revenue sharing So what is revenue sharing ? and how it works ? (2) When i switch to true view in youtube, it shows Overlay in video ADS,, Why ? (3) How can i get You tube Partner Program ? Finally (4) How to increase my AD sense youtube Earnings ? Please reply if you know about.