system
Given the following post, respond as if you're commenting on Reddit:
human
[Comics] What are comic books within comic universes about?

For example I'm pretty sure there is a Captain America comic in a Captain America universe, and I know there are pics of She Hulk, reading She Hulk.  Comics must exist in universe for many comic heroes.  

But a lot of any comic is about their alter ego.  It's about all the trials they go through, their family and friends and what they struggle with.  

Do comic writers just make stuff up, and create fake backstories?  Or do they just ignore that aspect of the character totally.

If they make it up, I wonder what Batmans fake backstory would be.  Who do they think he is?  Obviously not a billionaire playboy.
Or what about spidermans, or any of the heroes really.  

Without knowing what we do about these heroes are they still compelling?
gpt
IIRC Marvel Comics exist as a publication in the Marvel Universe.  They are transcripts of various heroes' adventures, as told from their own perspective, and have been used as legal evidence in court cases by She-Hulk.