"I am eating a big apple."
Translation:Jím velké jablko.
Ok, so why not "Jim jablko velke". Again, if the last word is the "stressed" in a comparison, it seems "big" would be it, i.e., what KIND of apple, not just ANY apple.
adjectives almost always go before their nouns in czech. the amount of focus your translation places on "velké" is on the level of "It is a big apple I am eating.", with the sentence stress shown by bolding.
if czech is the first flexible word order language for you, i recommend patience.