Turn on the watch. Go to Noise Buzz. You can make calls through dial pad, call log, favorite contacts.
Note: Make sure that Bluetooth call is connected at all times for a seamless Bluetooth call experience.

Make sure to add frequent/favourite contacts in the <app name> in order to access them on your watch.
In the Colorfit Ultra Buzz,

Go to contacts. Add up to 10 favourite contacts
Note: If the Bluetooth call is connected, all phone calls will be displayed on the watch synchronously.