In addition to that, it uses GPS, WiFi, and Bluetooth signals to pinpoint your location very precisely, and can use that to calculate the distances you travel and the number of steps it takes you to get there.
It can also put all of these data points together to tell things like your height and weight. It can only guesstimate things like your heart rate based on your age and BMI, but smartwatches these days have actual heart rate monitors, and pulse and oxygen meters built-in and can share that data with your phone.