• We use who for a person, and which for a thing or an idea. 
• We use that for both a person and a thing/idea. 
• Whose is a possessive pronoun. 
• When who is the object, whom, with a preposition, can be used instead, but it is formal and rather old-fashioned.      
  In modern speech, we use who, or we leave out the pronoun. 
• Where (relative adverb) refers to places. 

Examples of use :

• I know a woman. She speaks 6 languages.            »   I know a woman who speaks 6 languages. 
• I know a woman. Her husband speaks 6 languages. »    I know a woman whose husband speaks 6 languages. 
• I spoke to a person yesterday.                            »   The person to whom I spoke yesterday (formal)
                                                                    »   The person (who) I spoke to yesterday (informal)
• I live in a house.  It's 200 years old.                      »    I live in a house which is 200 years old. 

That's the hotel.  We stayed there last year.           »    That's the hotel where we stayed last year.              
                                                                       That's the hotel that we stayed in last year.