I watched the avengers before I watched pretty iron man 1 and 2, hulk and thor. I think I had watched First Avenger, but it's possible that was afterwards. Now, I've read the comics, so I was familiar with all the characters, but I followed what was going on in the movie pretty well. I will say that my enjoyment was enhanced once I'd seen the other movies, since I was a bit more familiar with the players (like, i didn't know that Hawkeye was introduced in Thor, so it was fun to see him there). I don't think you need to see every movie to understand what's going on (except for iw/endgame). As I've said, my parents haven't seen any other Marvel film, and they enjoyed Black Panther. I told them not to watch the end credit scene, since it wouldn't mean anything to them. Like, do you need to watch Winter Soldier to understand Guardians of the Galaxy? (to be fair, GOTG are the most disconnected marvel films) Do you need to have seen iron man 3 to understand....anything? Or Homecoming to understand Doctor Strange? Or Black Panther to understand Captain Marvel? Thinking about it, you really only need to see everything to really understand the avengers movies (and the captain america movies), rather than having to see every other movie to watch Captain Marvel.