Once in this screen, be careful to not pay for stable cards or packs unless you want them. There is a timer at the top screen that will cancel the booking if the booking is not processed within a certain time frame.
On the left of the screen, click Buy a Lesson unless you want to buy a pack of 10 lessons (stablecard) which gives you an extra lesson free. You can also buy Stablecards through Sharyn via email and she can invoice you directly and credit stable cards to your account should you prefer. If you choose to Buy Stablecard, then choose from the options on the right, otherwise hit Buy a Lesson and then you will be directed to the following page.