Summarize:

Once you become a lawful permanent resident of the U.S., you are advised to carry your Green Card with you at all times. This serves as your proof that you are authorized to live and work in the U.S. It also functions as a photo ID, much like a driver's license or passport. for more than 12 months at a time. Remaining outside of the U.S. for more than 12 months could result in the loss of lawful permanent resident status. If you need to be outside of the U.S. for longer than 12 months, you may need to apply for a re-entry permit prior to leaving the country. Green cards typically expire every 10 years. Plan to begin your green card renewal process 6 months prior to when your green card's expiration date. If you have a conditional green card, such as one based on a spouse or family member, you can apply to have the condition removed after 2 years.
Carry your Green Card with you at all times. Do not travel outside of the U.S. Renew your Green Card 6 months prior to expiration.