we use who/that to refer people
The man who/that rescued the children from the fire is a local hero
we use which/that to refer to objects or animals
The house which/that had the best-kept garden was photograped for a magazine
we use where to refer places
That's the town where they filmed the TV series
we use whose with people animals and things to show possession
This man whose dog barks all night
we use when to refer time usually after nouns such as time period moment day year and summer
August's the month when most people go on holiday
we use why to give a reason
He won't tell me why he quit his job