When you quote or paraphrase a specific passage from a source, you need to indicate the location of the passage in your in-text citation. If there are no page numbers (e.g. when citing a website), you can instead use section headings, paragraph numbers, or a combination of the two:
(Caulfield, 2019, “Linking” section, para. 1).
Section headings can be shortened if necessary. Kindle location numbers should not be used in ebook citations, as they are unreliable.
If you are referring to the source as a whole, it’s not necessary to include a page number or other marker.