There are two primary ways to become a US citizen: by birth in the US or by naturalization. To naturalize, one must generally be a lawful permanent resident for 5 years, meet residency requirements, demonstrate good moral character, pass English and civics tests, and take the Oath of Allegiance. US citizens can then sponsor relatives like spouses, children, and parents to become lawful permanent residents. However, the process involves forms, visas, background checks, and overcoming potential issues like proving a marriage is valid.