In most cases, an alien applying for naturalization fills out an N-400 Application for Naturalization. You can find Form N-400 here, and instructions to Form N-400 here. The alien applying must also submit a copy of the Alien Registration Card (green card) except in those narrow circumstances where one is not required. In addition, the alien must submit any supporting documentation that may be required in the alien's particular case, two identical recent passport sized photos, a filing fee, and a fingerprint fee. After filing the application, the alien will be notified of an appointment for fingerprinting. After fingerprinting is conducted, the USCIS will submit the fingerprint card to the FBI for a background check. If the alien's background is clear, then the alien applicant will receive a letter scheduling an interview with a USCIS officer. At this interview, the naturalization exams for English proficiency and knowledge of U.S. history are administered. In certain instances, USCIS will request that you bring additional documents to the interview. An examining officer determines whether the applicant satisfies all naturalization requirements and usually makes a decision on the interview date. If the decision is favorable, then the alien is scheduled for a swearing in date. After the alien is sworn in, he obtains a Certificate of Naturalization.
Sources:
M-476, A Guide to Naturalization
For other information about Naturalization, please click the following links: