This document provides examples of using prepositions of time such as "in", "at", and "on" with days, dates, seasons, and periods. It explains that these prepositions are used with expressions like "in the morning", "at night", and "on Monday". But they are not used when expressions involve "last", "next", "every", or "this". The document then provides exercises for the user to practice selecting the correct preposition of time in different contexts.