I recommend starting with his most popular and easily accessible short stories, the ones found in his classic Tales of Soldiers and Civilians (also known as In the Midst of Life). It contains his best Civil War and supernatural tales, including "An Occurrence at Owl Creek Bridge" and "A Watcher by the Dead." You can find them anywhere on the Internet and in scads of published editions. Of course, he also wrote scores of less well-known stories -- not to mention poetry, autobiography, and journalism. The Library of America published an extensive collection of Bierce's work in 2011 called The Devil's Dictionary, Tales, & Memoirs. There's a lot to discover.