Don't Install If You Want All the New Features
Apple announced many exciting watchOS 6 features at WWDC 2019, but not all of them are available on day one. This is still a developer beta that is aimed at making sure the new features for app support work. Developers can start building watchOS 6 compatible apps now and testing them on a real watch.
In the first beta there are some missing features, but this could change as Apple releases new betas. We often see new watchOS betas arrive every two to three weeks.
We often see Apple keep these features on hold even longer than the iOS and macOS features. You should also not expect every feature at full capacity -- especially those that work across devices. This includes the new Apple Watch features in macOS.