Two ways to be a legal US citizen, Citizen through birth, and Citizen through naturalization.
A naturalized citizen is one who is sponsored by a current US citizen and gets a green card to be here legally, and can then go through the process of becoming a US citizen.
Steps for naturalization. Prove you have had a permanent home in the US for 5 years, be at least 18, have knowledge of reading and writing English, and know the basics of US history and government. Be a person of good moral character. Complete your application, take a citizenship test, have a citizenship interview, finally, take the oath of allegiance.
Responsibilities- swear allegiance to the United States, serve the country when required, support and defend the constitution and laws of the US
Duties- vote, serve on a jury, pay income tax.