E. Relative Pronouns are: subject (people: who, things: which, people or things: that), object (people: who(m), things: which, people or things: that), and possessive (people: whose, things: which)
a. The Relative clause tells us which person or thing, or what kind of person or thing. (e.g. The woman who lives next door. ('who lives next door' tells us which woman))

E1. The Relative clauses can be used;
a. as a subject and avoid repeating the subject. (e.g. Isn’t that the woman who lives across the road from you?);
b. as object of a clause (e.g. Have you seen those people who we met on holiday?);
c. as object of a preposition, we usually put the preposition after the verb. (e.g. Who was the woman who you were talking to?)

E2. The Relative clauses in the sentence give us extra information about the person or thing, we use commas (,) with this clause. (e.g. We know a lot of people who live in London. vs. My brother Ken, who lives in London is a doctor)
a. as subject (e.g. My uncle, who was born in Hong Kong, lived most of his life overseas.);
b. as object (e.g. We saw the latest Harry Potter film, which we really enjoyed.);
c. as object of a clause (e.g. He finally met Paul McCartney, whom he had always admired.);
d. as object of a preposition (e.g. He decided to telephone Mrs. Jackson, who he had read about in the newspaper.)

E1. Relative Pronoun: Subject 
a. The Relative clauses can be used;
1. as a subject and avoid repeating the subject. (e.g. Isn’t that the woman who lives across the road from you?);
2. as object of a clause (e.g. Have you seen those people who we met on holiday?);
3. as object of a preposition, we usually put the preposition after the verb. (e.g. Who was the woman who you were talking to?)

b. The Relative clauses in the sentence give us extra information about the person or thing, we use commas (,) with this clause. (e.g. We know a lot of people who live in London. vs. My brother Ken, who lives in London is a doctor)
1. as subject (e.g. My uncle, who was born in Hong Kong, lived most of his life overseas.);
2. as object (e.g. We saw the latest Harry Potter film, which we really enjoyed.);
3. as object of a clause (e.g. He finally met Paul McCartney, whom he had always admired.);
4. as object of a preposition (e.g. He decided to telephone Mrs. Jackson, who he had read about in the newspaper.)

E2. Sometimes who(m)/ that/ which is the objective of the verb. (e.g. The woman who(m) I wanted to see was away on holiday. Who(m) (= the woman) is the objective, I is the subject)
a. When who(m)/ that/ which is the object, you can leave it out. (e.g. The woman I wanted to see was away. or The woman who(m) I wanted to see ~. Have you found the keys you lost? or ~ the keys that you lost?: the keys you lost (not the keys you lost them))
b. We can use that at the beginning of the clause. (e.g. I had an uncle in Germany that I inherited a bit of money from.)
c. the position of prepositions (in/ to/ for etc.) can be in the middle of the sentence or at the end of the sentence. (e.g. Bob is talking to a woman + do you know her? = Do you know her the woman (who/ that) Bob is talking to? Are these the books you were looking for? or ~ the books that/ which you were ~ = the books you were looking for (not the books you were looking for them))

E3. Whom is possible instead of who when it is the objective of the verb in the relative clause. (e.g. This is Peter, whom you met at our house last year.)
a. do not often use whom in spoken English, we often keep the preposition after the verb, and normally use who or that, or nothing (not whom) for people. (e.g. This is Peter’s brother, who I went to school with.)
b. can also use whom with a preposition (to whom/ from whom/ with whom etc.) (e.g. The people with whom I work are very nice. ( I work with them))
c. When whom or which have a preposition, the preposition can come at the beginning of the clause. (e.g. I had an uncle in Germany, from who/ whom I inherited a bit of money.) or at the end of the clause. (e.g. I had an uncle in Germany who/ whom I inherited a bit of money from.)
d. can use a preposition before whom (for people) and which (for things) -> to whom/ with whom/ about which/ without which etc. (e.g. Mr. Mike, to whom I spoke at the meeting, is very interested in our proposal.)
e. We often use quantifiers and numbers with Relative Pronouns (many of whom, most of whom, one of which, none of whom, some of which, lots of whom, two of which, etc.) We can use them as subject, object or object of a preposition. (e.g. She has three brothers two of whom are in the army.)
f. All of/ most of etc. + whom/ which: Bob has three brothers. All of them are married. (2 sentences) -> Bob has three brothers, all of whom are married. (1 sentence)

g. none of/ neither of/ any of/ either of, some of/ many of/ much of/ (a) few of, both of/ half of/ each of/ one of/ two of etc. + whom (people), + which (things)
1. can also say the cause of which/ the name of which etc. (e.g. The building was destroyed in a fire, the cause of which was never discovered.)
2. We can say: the day/ the year/ the time etc. 'something happens' or 'that something happens'. (e.g. Do you remember the day (that) we went to the zoo?)
3. We can say: the reason 'something happens' or 'that/ why something happens'. (e.g. The reason I'm phoning you is to ask your advice. (or The reason that I'm phoning/ The reason why I'm phoning))

E4. use Whose as the possessive form of who. (e.g. This is George, whose brother went to school with me. We saw some people whose car had broken down)

a. use whose mostly for people. (e.g. I met someone whose brother I went to school with. (I went to school with his/ her brother) I met man who knows you. (he knows you) vs. I met a man whose sister knows you. (his sister knows you) We met some people whose car had broken down. Ken, whose car had broken down, was in very bad mood.)

E5. can also use that (instead of who), but you can't use which for people. (e.g. Do you know anyone who/ that speaks French and Italian?)
a. cannot use that for people when we give extra information (e.g. John, who (not that) speaks French and Italian, works as a tourist guide.)
b. When we are talking about things, we use that or which (not who) in a Relative clause. (e.g. I don't like stories that have unhappy endings. (or stories which have~))
c. That is more usual than which, but sometimes you must use which. (e.g. Bob told me about his new job, which (not that) he's enjoying very much.)
d. can leave out who/ which/ that when it is the objective. (e.g. We stayed at the hotel (that/ which) you recommended.)
e. cannot leave out who or which when we give extra information. (e.g. We stayed at the Park Hotel, which a friend of ours recommended.)

E6. What = 'the thing(s) that': What happened was my fault. (= the thing that happened) (e.g. Did you hear what they said? (= the things that they said))
a. cannot use what in this sentences: Everything (that) they said was true. (not Everything what they said) (e.g. The machine that broke down is now working again. (not The machine what broke down. I gave her all the money (that) I had. (not all the money what I had))

b. Which (not what) = 'the fact that' Bob got the job, which surprised everybody. (1 sentence) which = 'the fact that he got the job'. We must use which (not what). (e.g. Ken couldn't meet us, which was a pity. (not what was a pity))
1. Using 'which' to give more information. We often use the Relative Pronoun which to say something about a clause. (e.g. He was usually late, which always annoyed his father.)

c. When (Time): We also use when with times to make it clear which time we are talking about. (e.g. England won the world cup in 1996. It was the year when we got married.)
1. but we can leave out the word when. (e.g. England won the world cup in 1996. It was the year we got married.)

d. Where (Places): We also use where with places to make it clear which place we are talking about. (e.g. I recently went back to the town where I grew up. (or ~ the town I grew up in or ~ the town that I grew up in) What's the name of the place where you went on holiday? Bob has just been to Sweden, where her daughter lives.)

more about the Pronoun ...