Also can some explain the post credit
Ok, so in the
comics, one of the original Captain Marvels pre-Carol Danvers, was basically a alien super being locked in the
negative zone and this fanboy named Rick Jones who was there at the hulk gamma experiment that turned hulk into hulk, ends up at some point with these arm BANGLES called the
negabands. When he would clank them together, he would swap places with Captain Marvel who would appear on earth and do superhero stuff, meanwhile Rick Jones would be trapped in the negative zone trying to survive, find a way out. Eventually he learns how to control it and swap on a dime and that's the gimmick with Rick Jones & Captain Marvel.
So
Considering that Ms. Marvel now has a bangle that makes her swap with MCU Captain Marvel, it just seems like they're pulling that Rick Jones/Captain Marvel storyline to use for The Marvels movie (except that Carol Danver Captain Marvel was probably not in the negative zone, just somewhere in the galaxy).
https://marvel.fandom.com/wiki/Nega-Bands