Just like with an iPhone, it’s simple to take a screenshot on your Apple Watch. It’s a similar process as on other Apple devices. To take a screenshot from an Apple Watch, go to the screen to take a screen capture of and then press and hold the digital crown (the round button that spins) while you press the side button down (the little button below the digital crown).
The screen will flash for just a second and you’ll hear the camera sound. If you wait a couple of minutes, the screenshot will automatically show up on your phone in the photo library.