what is a pronoun ?

A pronoun is a word used instead of a noun.
Eg: Mr Babu is a close friend of mine.
He is a clerk.
The first word in the second sentence is a pronoun used instead of the name 'Babu'

some commonly used pronouns.

I,you,we,they,he,she,it,myself,yourself,ourselves,themselves,itself,himself,herself,this,that,one,some,thing,something,someone.somebody,everybody,everything,anybody,anyone,anything,both,either,neither,none,no-one,nobody,these,those.