A pronoun is a word used instead of a noun (e.g. "he" instead of "John.". There are three main types: personal, reflexive and relative.
-Personal pronouns are of two kinds: subject (I, you, he/she/it, we, they) and object (me, you, him/her/it,us, them) Subject pronouns come before the verb, and object ones after ("I like him.")
-Reflexive pronouns (myself, yourself/selves, himself/herself/itself, ourselves, themselves) are similar to personal. The difference is that, as the name suggests, they can only "reflect" themselves – so you can say "He fancies himself" or "he fancies me", but not "he fancies myself."
-Relative pronouns are words like what, where, which, when, who and that:
"Do you know the name of the woman who left just now?"
"Here's the book that (or which) you asked for."
In these examples, who, that or which stand for the thing or person being discussed, which makes them pronouns. They are relative because they need the main clause ("e.g. "the name of the woman") in order to make sense, whereas "She left just now" makes grammatical sense on its own.