This is the 13147th most frequent Korean word.
두개
"두개" means "two things" in English.
The phrase '두 개' specifies quantity, meaning 'two', referring to the apples being eaten.
나는 사과 두 개를 먹었어요.
I ate two apples.
The phrase '두 개' demonstrates quantity ('two') of an object, which in this case are windows.
여기에는 창문이 두 개 있어요.
There are two windows here.
'두 개' is used to express the number of projects, indicating that two projects are being undertaken.