I know = 我知道
I see = 明白了
用法：
A君：He won't be coming with us.(他不会和我们一起去了）
B君：I know,he just told me.（我知道,他告诉我了）
--------------------------
A君：He won't be coming with us,he has something to be done.(他不会和我们一起去了,他有事）
B君：I see,we'll ask him out next time.（明白了,下次再约他出去吧）