Before you begin

• On your iPhone, go to Settings > Bluetooth and make sure that Bluetooth is on.
• Put on your Apple Watch, and keep your Apple Watch and iPhone close together as they sync.

Open the Apple Watch app on your iPhone

On your iPhone, tap Start Pairing, then tap it again on your Apple Watch. Wait for an animation to appear on your Apple Watch.

Hold your iPhone over the animation, then center the watch face in the viewfinder. Wait for a message to say that Your Apple Watch is Paired.

If you can't use the camera, tap Pair Apple Watch Manually, then follow the steps that appear.

Set up and pick a wrist

On your iPhone, tap Set Up as New Apple Watch. If you’ve set up before, you can tap Restore from Backup. Then choose which wrist you want to wear your Apple Watch on. Read the Terms and Conditions and tap Agree, then tap Agree again to continue.

If you see an Activation Lock screen, your Apple Watch is linked to an Apple ID. You need to enter the email address and password for that Apple ID to continue set up. If your Apple Watch was previously owned, you might need to contact the previous owner to remove Activation Lock.

Set up route tracking and Siri

Choose whether you want your Apple Watch to track your workout routes and the weather, which uses Location Services. Then choose whether to use Siri. If Siri isn’t already set up on your iPhone, it will turn on after you choose this option.

Then your Apple Watch shows you which settings it shares with your iPhone. If you turned on Find my iPhone, Location Services, Wi-Fi Calling, and Diagnostics for your iPhone, these settings automatically turn on for your Apple Watch.

Create a passcode

Tap Create a Passcode or Add a Long Passcode on your iPhone. Switch to your Apple Watch to enter your new code, then tap Yes or No to choose if unlocking your iPhone will also unlock your Apple Watch.

You'll also be asked to set up Apple Pay by adding a card.

Set up the Activity app and SOS

You can set up the Activity app by entering some information about yourself and setting your goals. If you already set up Activity on another Apple Watch, you won't get this step. If you skip this step, you can set up Activity later in the Apple Watch app on your iPhone.

Sync your apps

Wait for your iPhone and Apple Watch to sync. Depending on the amount of data you're syncing, this might take some time. Keep your devices close together until you hear a chime and feel a gentle tap from your Apple Watch.

Source: support.apple.com