Already is just a modifier emphasizing that it has already happened. The difference is between the present (I know) and the present perfect (I have known).
You would use the present tense when confronted with the something you've encounter beforehand.
I already know how to turn on the television.
I know how to drive a car.
You would use the present perfect to express something that happened previously, without specifying the time. You'll only use the present perfect and "already" when expressing previous events relative to the present.
I have been to France before.
I have already known many people before meeting you.
The past perfect is used to express something that happened before something else, without specifying the time.
I had gone to France before I went to Germany.
I had already known the story before I saw the film.