A mono earbud is included with Glass. Mono earbuds and stereo earbuds can also be bought from the Play store.
Here's how to put it on.
Plug the earbud in to the the micro USB port (the same port used to charge Glass). If you're putting on stereo earbuds, wrap the cord of the left earbud around the back of your neck. Push the cord into the earbud to create a loop you can adjust so it presses into the curve of the ear for a secure fit.
Slide the cord to adjust loop size for a better fit.
Feeling like switching it up a bit? Change the color of your earbud by replacing the cap.
Earbuds bought from the Glass store come with interchangeable colored caps. Replace caps by twisting them on to the outside of the earbud. Lefty loosey, righty tighty.
A mono earbud with a cotton cap is included with all Glass received after 10/28.