It’s important for your Apple Watch to have a solid charge before beginning this process. It can take a while for all of your apps and data to be synced to the device, so an ample supply of battery power is key. You can have your watch on its charger during setup, but some later steps work best while wearing the Apple Watch worn, so it’s best to charge it beforehand. 
Once your Apple Watch is at least 50% charged, the first step is simply to hold it, or the wrist it’s on, near your iPhone. If the Apple Watch isn’t already on, press the button below the digital crown and wait until the Apple logo appears before letting go. After a moment, you should see the “Bring iPhone near Apple Watch” animation begin to play on the wearable’s screen. 
Also: The simple way to add more complications to your Apple Watch
Once it’s on and near the iPhone you’re using for setup, a message should pop up on the smartphone’s screen with a Continue button. Tap this to get the process started.

Latest news
https://www.zdnet.com/article/how-to-set-up-an-apple-watch/