You can only watch on an Apple device. If you have an Apple TV, you can stream from the Apple Events channel found on the your home screen.
Everyone else can use a Mac, iPhone, or iPad and go to this link to watch. You must use the Safari browser though.
Apple will announce a new version of iOS, the operating system for iPhones and iPads today. The company will also announce a new version of OS X, the Mac operating system.
If you can't watch the live stream, be sure to stay tuned to Business Insider's tech page for live news and analysis.