There is no exact definition for "hot" but most people think a boy is hot if he has a good smile, an in-shape body, big eyes and shorter hair but not super short. Like I said, the term "hot" is very opinionated so this answer might not work for everything.
You nicely ask him out. If he says yes then on your date when you are alone tell him he is hot.
tell him hes handsome, or cute...
If you need it explained, then you aren't.
You can say "Eres atractivo" or "Me parece guapo" to tell a guy you think he is hot in Spanish.
Tell her you smell like roses
well she just feels it
Tell him u love him
if a guy thinks your hot he will hang around you and tell you that he thinks you look nice or say you have nice hair
I think your hot, wanna have sex?
ummm... TELL HER! girls almost ALWAYS wait for the guy to make the first move
I told my guy friend that he was hot:-) he said oh.
Tell him he is hot! Do it! I am telling you woman (or man)!!!!