Until recently you had to be accepted into the You Tube partner programme to be able to make money with ads on You Tube.
There has now been a change and you can now monetize video’s you have uploaded to You Tube a lot quicker.
If you sign into your You Tube account and click VIDEO MANAGER, You will see a link called MONETISATION.
Click that link and follow the instructions and as long as You Tube approve then you can start making money from your You Tube video’s.
Have a great day.