This document summarizes the uses of common Portuguese prepositions including: [1] At is used to indicate specific times, locations, or positions next to something. [2] In is used to indicate periods of time, locations within larger places like cities or countries, or positions inside something. [3] On is used to indicate days, dates, surfaces, or contact with something. The summary highlights the main uses and examples of at, in, and on in Portuguese based on the information provided in the document.