If you were admitted to the United States as a refugee, you are required by law to apply for a Green Card (Permanent Resident Card) in the United States one year after your admission as a refugee.
Naturalization is the manner in which a person not born in the United States voluntarily becomes a U.S. citizen.
If you were born outside of the United States, there are two general ways to obtain U.S. citizenship through U.S. citizen parents. You can acquire U.S. citizenship at birth (acquisition) or you can derive citizenship from your parents after your birth but before the age of 18 (derivation).
A Permanent Resident Card (USCIS Form I-551) is proof of your permanent resident status in the United States. It also serves as a valid identification document and proof that you are eligible to live and work in the United States.