Relative clauses

first: Relative pronoun

Who : it is a subject pronoun and we use it when we talk about people.
This is the guy who teaches me English. 

Whom: it is an object pronoun and we also use it when we talk about people. 
With whom did you come ?
From whom did you take it?
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Whose: use it when you talk about a possession. 
Whose pen is this?
This is the guy whose father teaches Physics.

Which: we use which if we talk about animals and things. We can use as a subject or object pronoun. 
Can you see that dog which is playing with a ball.

That: you can use it as a subject or object pronoun when you talk about people and things. 
He picked up the book that is on the shelf. 

Second: Relative adverbs 
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Relative adverbs are: when, where and why.

When: we use it when we refer to a time expression .
I recall the day when I  had my first car.

Where: we use it when we refer to a place.
This the cafe where I go to every day. 

Why: we use it when we mention a reason. 
This is the reason why i'm here tonight.