Your Apple Watch has gesture-based navigation that you can use to answer phone calls, move through menus, and select options on your screen. To enable hand gestures, go to the Watch app on your iPhone, open the My Watch tab, and go to Accessibility > VoiceOver > Hand Gestures. You can enable Hand Gestures on this page and go through the options under Customize Gestures.
The hand gestures Apple Watch recognizes are: Clench, Double Clench, Pinch, and Double Pinch. Closing your fist twice will answer phone calls on the Apple Watch, and overall these gestures are surprisingly functional.