How are you considered a citizen of the U.S?

a recognized legitimate nation state such as United States recognized you as a citizen of that state by passing all it's requirement.

How are you considered a troll of yahoo answers?

Well I guess you have that part figured out now

If you are born in the US, then you are a citizen. According to the 14th Amendment, "All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside."

Also, if your parents are citizens and you just happen to be born in another country, you are still a citizen. And you can become a naturalized citizen by going through the process.

Being actuall born in the United States.
or
Applying for Citizenship and taking the oath.

don't know