Your customer register is your list of all customers inside your system. From here you'll see all the information you have on each customer, when they logged in last time and what they have booked during their entire booking history. You can dive into their booking history by clicking on the person's "Bookings" tab. You can also view messages sent to this person by clicking on the "Messages" tab. Please note that if you haven't required your customers to register when making a bookin online or if you've created temporary users, they will not be visibile inside your customer register. You can also close a customer account from here after which the person will not be able to log into the system any more.
You can also find you admin personnel that have the right to log into the system from the customer register. You can give them different amounts of admin-stars (1-5) and depending on what is allowed to be done at each level they can do different things. You can define the required amount of stars per functionality from within Administration > Access Rights.
Inside the customer register you are also able to create dynamic groups, or Smart groups which will automatically include all people that fulfill the criteria set for that specific group. You can for instance create a group of all women over 35 years of age that have at least one haricut booking.