(1) Go to Settings (inside Sales) and Enable Sales.
(2) Then, go to Payments and choose one of the online payment gateways.
(3) After that, feel free to create a new Pricelist if you wish, or use the Pricelist already created with Bay Photo Labs.
(4) Once you have that set-up, go to your gallery, select Sales from the client options and Enable Sales by choosing a Pricelist to add to that gallery.
It's that simple. You can preview your gallery and the shopping cart will have been enabled. This will allow your clients to easily place an order.