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Use the video editing tools that YouTube provides after you've uploaded your video. You can add comments, links, or pauses to videos and during the pause you can add a link to another place or video.
 
YouTube will ASK you if they feel your videos warrant ads (translation, you only get ads if you can get enough views). You have to sign a contract saying you will only post original material, etc.
 
once your videos get around 15k views youtube will come to you and ask you if you are interested...

they have contacted me about 2 of my videos so far....
 
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