The core of Google Glass is its tiny prism display which sits not in your eyeline, but a little above it.
You can see what is on the display by glancing up. The glasses also have an embedded camera, microphone, GPS and, reportedly, use bone induction to give you sound.
Voice control is used to control the device; you say 'ok glass' to get a range of options including taking pictures, videos, send messages using speech to text, 'hang out' with people or get directions to somewhere