When should I fill in the Canonical URL on a page, and what does it do?

Usually you can leave it empty. Wcart then tells search engines that the page's own address is the main one.

Fill it in only when the same content lives at more than one address. For example, you might keep a copy of a page for a campaign. On the copy, put the full address of the original page (starting with https), so search engines treat the original as the main page and don't split ranking between the two.

To set it:

1. Go to Content → All Pages and click the pencil icon on the page.
2. In Meta details, fill in Canonical URL (optional).
3. Click Save changes.