"We have already introduced the general notion of enunciative level, relative to the use of direct speech in a text. Narrative levels are simply enunciative levels where the quoted speech is a narrative. A character in a story tells a story (about his past, for instance, or a fictional story) and that story is situated at a narrative level which is secondary with respect to the main story.
What Genette calls intradiegetic story is a story within a story,
not only in the sense that the first frames it with a preamble and a conclusion . . . but also in the sense that the narrator of the second narrative is already a character in the first one, and that the act of narrating which produces the second narrative is an event recounted in the first one." (https://www.unizar.es/departamentos/filologia_inglesa/garciala/publicaciones/structuralnarratology/4.Narration/4.6.Embedding.html)
These are notes from the above link, I hope they help in answering the question.