This document discusses prepositions of place and time in English. It provides examples of how to use the prepositions "in", "on", and "at" with places and times. For places, "in" is used for enclosed spaces, areas with defined boundaries, cities, and countries. "On" is used for floors of buildings, parts of rooms, and modes of transportation like boats and trains. "At" is used for certain locations like home, school, university, and specific places like doors and traffic lights. For times, "at" is used for specific hours, "in" is used for parts of days, months, seasons, and years, and "on" is used for days, specific dates