waht are the examples of common noun ?

A common noun names general items. It is a noun that can be preceded by the definite article (the) and that represents one or all of the members of a class. 

When one goes to the market, what all things does he/she see? Few instances might be refrigerator, ball, bat, chocolate, bicycle, potato, etc. All of these things are common nouns. 

Now, lets talk about places one might go. Few instances might be school, college, office, market, post-office, etc. All of these places are common nouns. 

We know so many people in this world. Father, mother, shopkeeper, driver, sister, tailor, etc. might be a few instances. All of these people are common nouns.