How to become an american citizen

        There are only two ways to become a U.S. citizenand that is either by law or by birth.
    If you are a citizen by birth, no action on your part is generally required (for example, if you were born in a state or territory of the United States), unless you were born to a U.S. citizen parent or parents overseas, and your birth was not recorded as a birth to U.S. citizens at a U.S. consulate overseas.    If you are not a U.S. citizen, then you seek to become one by naturalization, an process that requires you to take action and which is strictly governed by the Immigration and Nationality Act (INA).
     -- you may not become a naturalized U.S. citizen unless you:

    1.  Are at least 18 years old and a lawful permanent resident ("green card" holder);
    2.  Have resided continuously in the United States, having been lawfully admitted for permanent residence, for five years immediately preceding the date you filed your application for naturalization, or
    3.  Have, after having been removed from conditional permanent resident status, based upon your marriage to a U.S. citizen, having resided in the United States for one year after the date the condition was removed;
    4.  Have resided continuously in the United States at all times after your application to the time and date of your admission for citizenship;
    5.  Have, during all periods of time referred to above, been and still are a person of good moral character;
    6.  Have no outstanding deportation or removal order and no pending deportation or removal proceeding;
    7.  Have the ability to read, write, speak, and understand simple words and phrases in English;
    8.  Have knowledge and understanding of the fundamentals of U.S. history and government;
    9.  Are attached to, and can support, the principles of the U.S. Constitution and can swear allegiance to the United States.

http://www.visaus.com/citizen.html