Though this question should not be asked in the Q/A section.
Because there are already many posts in the forum that answer it.
and there is answer for this in the help section too.
Though I would like to tell you that when you are writing - Don't expect earning with it.
Because you won't earn anything by thinking that you'll earn something.
There are many people here who may/can write better than you and still they are not earning anything.
If you really want to earn something by writing - You should first check the quality of your writing.
If you can't write and post high quality posts then you should forget about earning anything.
The only way to improve writing is.
Read - Read - Read and Write - Write - Write.
Accumulate knowledge - That'll help you write high quality posts.
If you still want to know how to integrate those ads in your hubs then check this link - http://learningcenter.hubpages.com/generating-reve... -
It'll tell you how to do it :)