Having a greencard (permanent resident card) is a proof of being officially granted immigration benefits to live and work in the United States legally. You can work and live in the US permanently. Being a greencard holder additionally qualifies you for citizenship as permanent resident status is the primary eligibility requirement for citizenship.
Green card replacement application :
A permanent resident card (green card) is generally valid for ten years. You need to renew it on its expiration by filing Form I-90, Application for green card replacement with the USCIS. The same form is used when you want to change any biographic information on your card i.e if your name has changed due to marriage and also when you lose your card and need a green card replacement.
A conditional permanent resident should not be mistaken for a permanent resident. A conditional resident will get a greencard that is valid only for two years. He/She has to remove the conditions during the 90 days before the card expires. The conditional card cannot be renewed. The conditions must be removed else he/she will lose his/her permanent resident status. One has to file Form I-751 to remove the conditions. Once removed, you will get a permanent resident card that will be valid for the next ten years.
Per U.S. Citizenship & Immigration Services (USCIS, formerly the INS), if your Permanent Resident Card ("Green Card") has less than six months of remaining validity, you must renew your card prior to filing an application for naturalization.
After you send completed I-90 application to the USCIS, you can expect to receive an Application Receipt Notice with a 13-character Application Receipt number within 30 days. This Receipt Notice is the proof that USCIS has received your application and that it is being processed. You may use the number on the receipt to check the status of your application while it is pending. You will also be notified about your fingerprinting appointment and subsequently, your interview date with instructions related to the supporting documents you need to bring. The entire green card replacement process nearly takes three months.