Pronouns

There are several words that are used to replace nouns. They are called pronouns. Pro in Greek means "for" or "in place of". Some are called personal pronouns because they take the place of specific names of persons, places, or thing, as in: Has Fred arrived? Yes, he is here. Here he is the personal pronoun that replaces Fred. As indicated in the table, there are both subject and object personal pronouns as well as those that show possession. In His house is the white and green one, his is a personal possessive pronoun.

Personal pronouns: subjects, objects and possessives
Singular	Subject	Object	Possessive
First person	I	me	my, mine
Second person	you	you	your, yours
Third person	he, she, it (one)	him, her, it (one)	his, her, hers, its (one's)
Plural	Subject	Object	Possessive
First person	we	us	our, ours
Second person	you	you	your, yours
Third person	they	them	their, theirs*

*Some authorities give my, your, his, her, our, your and their as possessive adjectives or pronominal adjectives, as they qualify nouns.
Some personal pronouns are formed by the addition of -self or -selves as a suffix: myself, ourselves, yourself, himself, herself, itself, and themselves.
Demonstrative pronouns - this, that, these, those - refer to particular people or things. This is mine, and that is yours. The demonstrative words can also be used as adjectives: this house, those cars.
Pronouns that refer to people or things in general are called indefinite pronouns. Like the demonstrative pronouns, they can be used as adjectives: another day, both animals, many weeks.
The words who, whose, whom, that, which, and what are called relative pronouns. (The word that can be a demonstrative or a relative pronoun.) They create relative clauses in a sentence: The committee, which met last night, discussed your report. The words which met last night form a relative clause that describes the subject of the main clause, the committee.
When a relative pronoun is used as the subject of a sentence such as Who ate the pizza?, it is classed as an interrogative pronoun. Interrogate means “ask” (questions).

source:http://babelnet.sbg.ac.at/themepark/grammar/pronouns.htm