We use THIS (SINGULAR) (1) to talk about things or people near us, (2) to introduce people, (3) to begin a conversation on the telephone, (4) to refer to the present time:
(1) Look at this dog over here. (2) John, this is Jim. Hi, nice to meet you. (3) Hello, this is David speaking. (4) I saw him this morning.
We use THAT (SINGULAR) to talk about: (1) things or people that are not near us, (2) something that has happened, (3) what somebody has just said, (4) a past time or event
(1) Look at that cat over there. (2) I'm sorry I'm late. That's all right. (3) I'm going to Spain. Oh, that's nice. (4) That girl I met last night was silly.
We use THESE (PLURAL) to talk about things or people near us:
Come here! These rings are beautiful.
We use THOSE (PLURAL) to talk about things or people that are not near us: