If you bought this phone secondhand it may still be linked to the previous owner's ID and you're encountering this --> "Activation Lock for iPhone, iPad, and iPod touch" is a security feature with an aspect of possibly deterring re-selling of stolen devices. To learn more click here --> http://support.apple.com/HT201365
An activation lock can only be removed using information for the account that applied the lock. Click on this link to learn 'How to remove Activation Lock' --> https://support.apple.com/HT201441
If you do not know the required information and you are not the original owner, get the owner of the account to remove the lock or return the device for a refund or recycle it. The device is otherwise useless to you. If the owner is unknown and has not provided contact information as a message showing in the login screen, there is no way to contact the owner unless the person who gave you the device knows them.