After you have successfully paired your Gear S3 watch with your Android phone, and downloaded the Glympse app to your Gear S3 watch and phone, it's time to launch Glympse on your Gear S3!
Tap the Glympse icon on your Gear S3 and you should see the message "Please pair with the Glympse app on your phone to link account info".
Open your Android phone and open the notifications center. You should see a notification titled "Account linking. Tap to link Glympse on your Samsung Gear device". Tap this notification. Doing so will trigger a pop-up menu with the option to link Glympse. Tap Link Now, and look for the confirmation on your Gear S3 watch. You are now ready to use Glympse on your Gear S3!