One song, really?

I guess what I’m not getting is how is the school determining “you’re a good fit” for our program? Like they hear you sing, they hear your monologue and then is it just going by your essay you wrote? Do most schools then do an interview to access “fit” ? I keep hearing this and I guess I’m not understanding fit. I know they can tell" type " by your appearance and resume and audition but this fit thing is not clear to me.