Similar to the previous watchOS 2 Beta 3 release, the fourth build of watchOS 2 is also considered a minor update, since it only features bug fixes as well as under-the -hood improvements. However, watchOS 2 is the first major software update to hit the Apple Watch, featuring native apps, new watch faces including photo albums and time-lapse, Complication, Time Travel for viewing previous as well as upcoming events, Nightstand mode, and much more.
You can get watchOS 2 Beta 4 through Software Update from an iPhone running iOS 9, by going to the Apple Watch app > General > Software Update, or from the Watch Dev Center for registered devs.
