when you knock at someone's door.....and on asking what would you say.....its i or its me???
Technically, it would be "It is I."
But, no one says that. Today, people say "It's me".
In fact, if someone knocked at my door and replied "it is I" after I asked who was there, I probably wouldn't open the door.
NOT A TEACHER
(1) As the teachers have told you, most people nowadays would use "me."
(2) This non-teacher respectfully suggests that you follow the rule:
It is I, he, she, we, they.
(3) I assume that you are studying English because you wish to communicate
with native speakers. The more educated native speakers will feel more respect
for you when they notice that you know the rule.
(4) This is only my opinion, which is shared by only a few other people. (I suspect
that some university professors who write scholarly books also follow the rule -- even
those professors who may say that the rule is not important or old-fashioned.)