Foam padding: comfort so you can enjoy VR for longer.
HD display: so you can see stuff.
Circuit board:converts HDMI to display driver which drives the HD display also contains a Inertial measurement unit IMU which contains: accelerators and a magnetometer.
Cover: makes sure that the insides of the VR headset don't tumble out , it also contains (depending on the model) IR LED's for position tracking.
Dial: Moves the HD display move back and forth to focus and unfocused the view.
Lenses: To make it look clear and this will be explained better later on.
lenses help you see things that are too close to you to normally see by making it look further away, but still keeping the wide view.
Having no lenses is like trying to play a game on a iPad that is right in your face .
Lenses are really just specially shaped prisms