Hi
Yes - Apple Watch signs in to iCloud using the same Apple ID account as the paired iPhone:
Set up your Apple Watch - Apple Support
It can also be protected by Activation Lock:
About Activation Lock on your Apple Watch - Apple Support
The functions that are available on Apple Watch when it is away from the paired iPhone depend on various factors including:
- Your Apple Watch model:
- The features of your carrier service plan:
- The type of connectivity that is available to your Apple Watch at the time:
About Bluetooth, Wi-Fi, and cellular on your Apple Watch - Apple Support
Features and requirements that apply under various circumstances are detailed here, including within the footnotes:
How to use your Apple Watch without your iPhone nearby - Apple Support