***I'm not a teacher***
You use this is...to introduce people, e.g. somebody starts:
-nyota, this is faryan.
-Hello faryan - pleased to meet you.
Or on the phone:
-Hello, this is nyota.
When you introduce *yourself* you don't say "this is..." but rather: I'm nyota or My name is nyota.
When you're home alone and you hear somebody come in you can ask,
-It's just me.
You're at a party and you see somebody you don't know, so you ask your friend,
-Oh, that's my sister, do you want me to introduce you?
- Who's that girl?
- She's my sister.
- Who's that (over there)?
- It's Jake Smith. You know Jake, the one who helped you carry the bags.