To book an appointment, you need to add product to your online store which was created in "Shopify Products" when you created virtual or inperson appointment in the Servv app.
Once you add product to your store, the customers can come and select the product to book an appointment.
After they select the product, they can see an option to "Select Date and Time" for an appointment.
When they select the button a calendar widget will open, showing the available dates and the time slot slots for an appointment. A customer can pick one date and time and book an appointment.
They can confirm and proceed for a payment (for paid appointments) to complete the booking process.
Other articles to refer to for more information about booking virtual appointments:
Automate email notification for appointment booking