Either the dial or swiping can be used to navigate between screens. You access widgets right of the watchface and notifications left of the watchface. You can use the dial to select an app, a button on the side to take a step back or a different button on the side to return to the homescreen.
S2 runs Samsung's own Tizen operating system. It currently has a lot less apps than Android Wear or Apple's Watch OS and a lot of third-party apps perform badly on the device. It's unclear if developers will start to develop Tizen apps in the near future.