to be small - difference between verb and adjective?

Hi there,

it is 1 a.m. and it was a long day, maybe this is why I'm getting so confused and totally crazy! But:

I was just studying around in a foreign language, where stupid grammar things pop up more explicitly. Now I was just for fun making up a sentence about a friend, "You are small" ;), because the language exercise highlighty specialties concerning verbs vs. adjectives.

But actually concerning e. g. (!) to BE small, I wonder where is the difference?

I mean considering "to be small" what is the verb and what is the adjective?

I don't see the difference currently! O.o ...I think I am very tired. What is my problem? ^.^

After a bit of thought I think here I just need to ignore the adjective, as I can't attribute an adjective to a person (and their physical characteristics) whatsoever, right?

(On a sidenote, the language is Korean, whereas: > “adjectives” are presented in the form of “descriptive verbs” in Korean, [...] adjectives never change forms < while 작다 [ jak-da] = to be small, while I wonder about why my textbook notes "to be small" as 작아요 (and not 작다요), while from my understanding this is a contradiction (i.e. wrong), if the quote above is factually correct?!)