Literature notes in the Zettelkasten combine ideas from your [[source-notes-in-the-zettelkasten-method-of-note-taking]]❌ in such a way that you can revisit them later and fully understand them without the need to refer to the source material.
As an example, if you are researching the topic “Baking a chocolate cake” and you use three different source materials, you would take relevant quotes from the sources into separate Reference notes for each source, then combine what you have learned from these sources into a single literature note, written in your own words, with links back to the original source.