The feature isn't available for everyone just yet, but it is now live for at least some users (via MSPU) following an update to the app, and should gradually make its way to others soon. Once available, however, you should be able to go live by swiping right to access your Story camera. From there, you can switch to Instagram Live with a toggle at the bottom of the screen and start broadcasting.
You can, of course, also check out Instagram Live videos from your friends in the Stories bar at the top of your feed, and from other Instagram users in the Explore section of the app. This is on top of new Snapchat-like features for Instagram Direct, which you can now use to send pictures to others that disappear after opening.
Have you seen the Instagram Live feature pop up in your app yet? Let us know what you think in the comments!
Thanks, Sed P. for the tip!