One of the easiest way to access the camera on Galaxy Note 4 is to use the camera shortcut on the lock screen. To remove / add camera shortcut to lock screen on Note 4 do as follows:
1. Open Settings and go to the Device tab
2. Tap to open the Lock Screen settings
3. Regardless of the screen security you've selected, you should see the Camera Shortcut option.
4. To add camera shortcut on Galaxy Note 4 lock screen, you just need to mark the mentioned option (and to remove, unmark the option)