I'm guessing you are referring to the naturalization process of the united states, so I'll just go with that. To be eligible, you must be 18, be in the country lawfully, have lived in the US for at least 5 years at the time of application, and be of good moral character.
You then fill out applications with your attorney which also includes pictures of yourself and other documents.
Then you are fingerprinted
After that, you go to an interview and take 2 two tests: English and civics
finally, you take an oath of allegience.