Hello @DavidJackson491
I believe that you are referring to creating what is referred to as a: Jump Link. A Jump Link is a link that 'jumps' to a specific section of a page on your website. External links, however, are hyperlinks that direct users to a page on a different website.
There isn't any official Canvas documentation on how to create a jump link, but I was able to locate THIS third party resource on Jump Links and how to create them.
The Rich Content editor in Canvas should allow you to add jump links to buttons you create in various area of Canvas, such as pages.
Hopefully this helps!
-Colton