Form N-400

Form N-400 is used to apply for US citizenship through the naturalization process. Lawful permanent residents (also known as green card holders) of the United States, who meet the eligibility requirements, can file N-400 form to request citizenship. In the United States, 8.8 million Lawful Permanent Residents are eligible to naturalize.
Becoming an American citizen gives the same rights and privileges of citizenship as natural born American citizens, except one: naturalized U.S. citizens are not eligible for the Office of the President of the United States.
US citizenship eligibility requirements.
To be able to apply for citizenship through naturalization, you have to meet the following requirements. You must:
Content.
The N-400 form is a series of questions about eligibility, personal information, marital history, children, criminal activities and the oath of allegiance to the United States. Many services, on the web, help candidates to the naturalization to fill the form. Sometimes, a lawyer's help is required.
Filing the form costs $640 along with an $85 bio-metric fee for a total of $725, where applicable. Exceptions can be seen on the federal website.
After filing the form, the applicant undergoes an interview process with the United States Citizenship and Immigration Services (USCIS). The USCIS interview includes an English and civics test. The English test has three components: reading, writing, and speaking. The civics test covers important U.S. history and government topics.