1. Who - Used for people
Example : The woman who called yesterday wants to buy the house.
2. Which - Used for things and animals
Example : Did you see the letter which came today?
I love the puppy which is jumping at the kitchen.
3. That - Used for people, things, and animals (who and which can be replaced by that, which we use commonly in spoken English)
Example : The girl that we met in France has sent us a card. (or who)
We live in a ground floor flat that backs onto a busy street. (or which)
Do you like the cat that is sleeping underneath the table? (or which)
4. Whose - Used for possessions of people, animals
Example : He’s a man whose opinion I respect.
She’s the student whose handwriting is the best in my class.
5. Whom - Used for people when the person is the object of the verb
Example :The author whom you criticized in your review has written a letter in reply.