-Who/that: Who is more common.
EX:The man who killed your father has been arrested.
EX:This is the man who hit me.
That is possible after all/everyone/everybody/no one/nobody:
EX:Everybody that knew him hated him.
The object form is (whom) but (who) is possible.
EX:The man whom/who I met told me about the crime.
EX:The man I met told me about the crime.(It is possible to ommit the relative pronoun here.)
-Which/that:(which is more formal)
EX:That is the cat which/that ate the fish.
EX:The motorbicycle which/that I hired broke down.It is possible to ommit the relative pronoun here as follows:
The motorbike I hired broke down.
We use that not which after all/everything/little/much/no/none and after the superlative degree:
EX:This is the most exciting film that I have ever seen.
EX:All the oranges that fall are eaten by my son.
-Whose(for possession)
EX: I visited my uncle.His farm is full of trees.
Here we ommit his from the second clause and put whose:
I visited my uncle whose farm is full of trees.
-Where(for place)
EX: This is the country.I lived in it.
Here we ommit in it and use where.Where is put at the beginning of the second clause.
This is the country where I lived.
-Note that Where relplaces there /here/in/in it.
-When(for time)
EX: I was praying at 8 o'clock.My phone was ringing at that time.
I was praying at 8 o'clock when my phone was ringing.
Here we ommited at that time and put when at the beginning of the second clause.