Won't и will not be? В чем отличие? Когда надо писать won't, а когда - will not be? Ответьте, пожалуйста.

Won't = will not
То есть won't - это краткая отрицательная форма вспомогательного глагола will с отрицательной частицей not. Так же, как, например, do not = don't, is not = isn't, have not = haven't
I will not be at school tomorrow. = I won't be at school tomorrow.
He will not come. = He won't come.