YouTube sharing program has all the information on the site. If I'm not mistaken I think you have to be eligible or approved.
It use to just be that you had to be a YouTube partner in order to put ads on your video and to become a YouTube partner you had to have a certain amount of subs and views on your videos. Just last summer they started letting non-partners put ads on their videos. I only have 600+ subs but I am allowed to submit each of my videos for revenue sharing, almost all of them get approved and my views range from 50-1000views+, unless I use a song or something. The other way is to make a video and it goes viral, then they will let you monetize it(unless it uses copyright materials).
If you can manage to get a lot of viewers, you could end up making a decent amount of cash with YT's rev. share system. However, your videos have to be viewed as non-spammy. Youtube is cracking down on videos which don't offer any value, however they perceive value. Alot of people have been getting their accounts shut down without warning. So make decent videos and build a following or subs. Good luck.
There are many helpful articles on the youtube help site. More information provided on monetization and how it works: http://support.google.com/youtube/bin/topic.py?hl=en&topic=1311104