To enable the e-commerce feature you have to add digital photo products. To do so go to e-commerce in the menu of your CMS and select 'Products'.
To add a digital photo product click the blue button that says 'Add product'. A new product will appear, to set up the product click the 'pencil' button at the right of the line. Now fill in all the required fields and click 'Save' at the right bottom.
Per photographer it is possible to add different products, this allows you to handle different online prices when you have different locations.
If you want to disable the e-commerce feature, go to 'Settings' - 'Photo Website' in the sidebar of your CMS. Select the theme of your Photo Website and click the pencil at the end of the line to edit. Scroll down and deselect the 'Webshop enabled' box.