how do y'all know you have a crush on someone?

im not really a kid(I'm in my late teens) but i genuinely have no idea how to even know if I have a crush on a person.

here's the situation, there's this guy in my class, we've talked a few times, not much but I feel like I might have a thing for him?

is there smth like a checklist for me to know that ooh i like this person?