How do I unlock iPad
How do I unlock iPad when found
[Re-Titled by Moderator]
iPad Air, iOS 12
What kind of lock?
Find My iPhone Activation Lock - This is a security feature, in part to deter re-selling of stolen devices.
http://support.apple.com/HT201365
Turn off Find My iPhone Activation Lock (formerly: Activation Lock: Removing a device from a previous owner’s account) - An activation lock can only be removed using the log-in information for the account that applied the lock.
https://support.apple.com/HT201441
Get the owner of the account to remove the lock or return the device for a refund. It is otherwise useless to you.
If the owner 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.