Why do I have to subscribe to apple fitness? I thought it was part of the device. I just want to track my activity levels. do I have to pay for that?

Apple Fitness+ is an optional paid service that gives you access to guided workouts from 10 categories. You can continue to use Apple Watch and the Fitness app for free just as you used to to track the status of your rings, see workout history, view activity trends, and earn awards.

Apple Fitness+ is a different service. You can track your movement, exercise, workouts, steps, etc. as just part of the device.