You can tell Glass to do lots of things like a Google search, take a picture, record a video, get directions, send a message, and make a call. All you have to do is say the magic words "ok glass" and then say your voice action aloud.
Glass must be activated and your display must be on in order to start a voice action. To get Glass to wake up and listen, tap the touchpad once or lift your head to the Head Wake angle (if you have Head Wake Up on).
Once you say "ok glass," you'll see all available voice actions. Scroll through this list by tilting your head up or down.
You can also tap the touchpad while on your Home screen to open the voice action list without speaking. Once you do, you can scroll through the available list of actions using the touchpad. The touch menu looks a little different than the voice-activated menu; the actions are listed horizontally rather than vertically. However, the list of actions and their functions are the same.
Continue through this guide to learn some more Glass voice actions.