Hi Rupert,
Thanks for your question. An SSL certificate is not required for WooCommerce to function, but I highly suggest using one on your site for two reasons:
Customers are savvy enough to know that when they see "https:" in the URL of their browser that the personal data they are entering on a site is protected. This gives them more confidence when making a purchase.
The goal of the SSL certificate is to protect your customer's information.
Added confidence from customers and search engines is enough of a reason to install one on your site. You can contact your web host for instructions on getting an SSL certificate added to your hosting account.
When I mentioned WooCommerce would protect the downloadable files on your site I was referring to direct access to the files. WooCommerce stores the ebooks files in a directory that prevents someone from guessing the file name and attempting to get the file by typing in a URL like: http://www.sample.com/wp-content/uploads/ebook1.zip
I am actually just selling ebooks so I don’t know if I still need SSL certificate installed on my site. On the Woocommerce videos however, Daniel said that my web server will protect my files. I guess I need further elaboration on this very important point. Thanks for the usual assistance. I really appreciate it.