what does iphone locked/unlocked?

if it's locked you can't use it until you unlock it, unlock it by dragging your finger across the bottom of the screen.

Hi iphone locked is nothing but the iphone is locked to a particular network provider due to this it wont accept any other GSM sim until you unlock it ...Unlocked iphone is nothing iphone which is already from network provider so you can freely use it with any GSM sim ..If you want to unlock iphone from network provider then i will refer you to visit sites like Unlock-Zone.com here they are rendering remote unlocking service to unlock all model iphone from network provider .You first verify that whether the service is available for your country and network provider if yes then purchase the service then visit sites like MobileUnlockGuide.com to get free instruction about how to use that service and unlock your iphone ..After unlocking it you can freely use it with any GSM sim ...