To favourite a practitioner, navigate to the practitioner's profile page. You will see a heart beside the name of the practitioner. Click once on the heart. If you're not logged in, the login screen will pop up. You need to be logged in to favourite a practitioner. If you are logged in, the heart will be highlighted and the practitioner has been added to your favourites.
To view or manage your favourites, click on the the 'My Favourites' button at the top right of the screen.