In the Book l of Ethics, Aristotle is searching for the source of human happiness. He is trying to explain what is “good happiness” and we can archive that happiness. Aristotle in some way said that the function of a human being is related to the good.

Some people agree to call the good happiness. Every sort of knowledge and decision pursues well. They say that living well and doing well is the same thing as being happy. But in another way some people used to thinks that there are more goods than the ones presented before. They think that there is some good that is good in itself, and that thing that is good in itself is what causes all the things to be good. Aristotle says that since happiness is the end of the things pursued in actions, therefore, we need to look for what makes the human being happy to found human happiness. He starts his research looking for the human function. He says that every part of the human body seems to have some special action and function. So now he is looking for a function of the human being. He found that the function of the human being is to reasoning and living a noble life. Happiness requires a complete virtue, a complete life. We cannot call a human being happy during his lifetime.
In conclusion, happiness is something that depends on ourselves. We need external activities to achieve happiness. We always believe that having things and doing well is happiness well is part of happiness, but actually happiness is more like performing the activity or the function. Happiness also depends in the cultivation of virtue. If you have a complete virtue you have a complete life.