(used to indicate a person, thing, idea, state, event, time, remark, etc., as present, near, just mentioned or pointed out, supposed to be understood, or by way of emphasis): This is my coat.
(used to indicate one of two or more persons, things, etc., referring to the one nearer in place, time, or thought; opposed to that): This is Liza and that is Amy.
(used to indicate one of two or more persons, things, etc., implying a contrast or contradistinction; opposed to that): I'd take that instead of this.
what is about to follow: Now hear this! Watch this!
(used to indicate a person, place, thing, or degree as present, near, just indicated or mentioned, or as well-known or characteristic): These people are my friends. This problem has worried me for a long time.