I locked my iPad using iCloud. How can I unlock this?

I use my iPad I must enter a code

Do you mean a passcode to unlock the iPad like you see here > iPad: Wrong passcode results in red disabled screen

If you can't remember the Passcode, you need to restore the device from the computer it was last synced with.

Follow the instructions for putting the device in recovery mode > Unable to update or restore

OR, the password for your Apple ID for iCloud? If it's your Apple iD password, help here > Apple - My Apple ID