A preposition is a word which is used to link a noun to another word in a sentence.
Prepostion is usually placed before a noun or pronoun.
Some examples of Preposition are - 
At, After, About, As, Above, By, Between, Expect, In, Inside, For, Of, On, To, Under, Near, With, Without, Within, etc.



Some sentences showing the use of preposition are given below -
1. We went to school.
2. He lives in Delhi.
3. Pen is on the table.
4. They are coming from market.
5. He is standing under the tree.

Here are some pictorial examples which will help you understand the usage of Preposition in a better way.