Prepositions "On," "At," and "In" A preposition is a word that links a noun, pronoun, or noun phrase to some other part of the sentence. Prepositions can be tricky for English learners. There is no definite rule or formula for choosing a preposition. In the beginning stage of learning the language, you should try to identify a preposition when reading or listening in English and recognize its usage. to the office at the desk on the table in an hour about myself A preposition is used to show direction, location, or time, or to introduce an object. Here are a few common prepositions and examples. On Used to express a surface of something: I put an egg on the kitchen table. The paper is on my desk. Used to specify days and dates: The garbage truck comes on Wednesdays. I was born on the 14th day of June in 1988. Used to indicate a device or machine, such as a phone or computer: He is on the phone right now. She has been on the computer