@Marylew: The best way to do this would be via the Galaxy Wearable app. This may be pre-installed on your phone, so please swipe up from your Home screen, tap on the Samsung folder, and look for it here. Alternatively, you can download the app for free from the Google Play Store.
To pair your watch, simply open the Galaxy Wearable app, tap on 'Start the journey' and follow the on-screen instructions. For further clarity, please take a look at the guide in the link below.