Google has released MyGlass, an iPhone companion app for their Google Glass headset. MyGlass is used to pair and manage Glass right on your iPhone, including determining what notifications your receive, like Gmail and Google Now. The app includes some instructional videos, including how to turn on and wear Glass, as well as how to pair it with your phone. The app will look to see if personal hotspot is enabled on your phone, though you can elect to set up Glass via Wi-Fi instead. A Google Glass update, XE12, is rolling out today with support for MyGlass, so you will need to update Glass before you're able to use the app.
The app is free, but requires a Google Glass headset to use. It can be downloaded now from the App Store.
Update: The app itself isn't actually available at present, but Google says it should be available later this week. It'll be available at the link below when it goes live.