You get a the symbol [1] to the left of the Safari search bar. When you are on a site like ancestry, you click that and it brings up a menu of things to do. There are options to search other sites when you are on a WT profile page or on an Ancestry/FamilySearch/etc. page it will have the option to build the citation which gets copied to the clipboard so you can paste it into a profile. You will also want to explore the various settings in order to get the style citation that you want. It accomplishes this by reading through the page it is looking at and finding the relevant information.
When it creates a citation, it already has the <ref></ref> tags there so just pasting it in place if you select the inline option. The other option is a bullet list citation.