Once the feature is enabled, you can customize the settings and increase the contrast, customize the menu, and more. Tapping on the Hand Gestures toggle turns on the feature and also allows you to customize the gestures if you so desire. By default, a pinch will take you to the next item on the screen. A double pinch will take you back one item.
If you forget what each gesture does, you can always return to the Apple Watch accessibility menu for a quick refresher. Or why not bookmark this story on your browser so that you can refer to it when you need to?