on the #mastodon subreddit I see lots of things like:

"I have an account on server.foo. I was on server.bar and I wanted to follow someone so it prompted me to log in. But it didn't work when I tried to log in with my server.foo account credentials"

look, I know it's complicated, especially if you're new, and I don't even really blame the user... it's just that seeing people knowingly entering login credentials for one site into another unfamiliar site, idk what to even say to that