First, your customer needs to have been invited to the Portal, as per the steps described here. 

Next, a login to the portal is required - this is simply done by visiting your Portal URL and entering the necessary login credentials. 

Once logged in, go to My Bookings, in the main menu. Here is where you can book a meeting room or a desk; and also view your bookings after having made them.

On the left side of your screen, there is a Calendar where you can select the date on which you would like to make the booking. Below, you can select the Location and Centre where you would like to book, as well as the number of people you need the room to accommodate, the room layout and timescale.

The available rooms and timeslots will then be listed on the right side of your screen. Click the timeslot that you would like to book.

Next, you will be preseted with a confirmation screen where you can adjust at what time you would like to book, as well as for how long. Click Book, if you would like to book the room without adding sny services.

If you would like to add services to your booking, click Add Services. You will then see a list of available services you can add to your booking. You can see their price and can adjust the quantity you require. 

Once you complete adding services, click Book Room. If you have changed your mind, click Go back to restart your booking. 

Once you select to book, a summary will be displayed - please verify your booking details, check that you have read and accepted the Terms and Conditions, as well as the Privacy Policy. Click Pay when you are ready to submit your payment.  

Enter the payment information on the next screen. 

Click Review Transaction, verify the information, then Submit the payment.