The best general history/introduction to the Rising itself is The Rising: Easter 1916 by Fearghal McGarry. For a more expansive coverage of events, The Irish Revolution, 1916-1923 by Marie Coleman is another good book to check out. There is also a vast corpus of scholarship that delves into specialized topics of the Rising. When History Was Made: The Women of 1916 by Ruth Taillon is a history of the many women that took part in events. The recent book Children of the Rising: The Untold Story of the Young Lives Lost During Easter 1916 by Joe Duffy examines children in the events of 1916. Each of the leaders of the Rising has at least one biography. Tim Pat Coogan's biographies of De Vallera and Collins are accessible entry-level biographies of these two famous figures that came out of the Rising.