Interfaces allow snaps to communicate or share resources according to a protocol defined by the interface. For example, the serial port interface is offered by the Ubuntu Core snap to let other snaps access the serial port of your board or computer.
Offered by the Ubuntu Core snap to give your snap access to the serial port. Use this as a reference when you build your own interface.
Offered by the Bluez snap to give your snap access to Bluetooth.
A basic implementation offered by the Ubuntu Core snap to give your snap access to the camera.