Question

what do you mean by a preposition, where is it used ?

Answer 1

A Preposition is a word which is placed before a Noun (or a Pronoun) to show the relation in which the person or thing denoted by the noun stands to something else.
1. a book is on the table.
2.She was very kind to us all.
3. Tom agreed with me on that point.
4. The people were alarmed at  this news.