Prepositions provide important information about the relationship between things. A preposition shows how a noun, pronoun, or phrase is connected to other words in a sentence. Common prepositions include words indicating location like "on", "in", "under", as well as time words like "until" and "during". Prepositions also convey position, direction of travel, and other spatial relationships. Writers should choose prepositions carefully to ensure they make sense in context and consider alternatives that may enhance their writing.