A Time-Turner may be used for short-term time travel. Hermione receives a Time-Turner from McGonagall in Prisoner of Azkaban, enabling her to attend more than one class simultaneously. Hermione is ordered to keep it a secret from everyone, including Harry and Ron, although they do notice the suspicious impossibility of her schedule and several bizarre disappearances and reappearances. Hermione lets Harry and Ron in on the secret near the end of the book, when she and Harry use the Time-Turner to save Sirius Black and Buckbeak. Feeling the strain from her heavy course load, she finally returns the device to McGonagall at the end of the novel.
A large supply of Time-Turners is kept at the Ministry, as seen in Order of the Phoenix; however, during the events of that book, a glass-fronted cabinet containing the Time-Turners is destroyed. Due to their time-affecting properties, the cabinet is seen to fall, shatter and repair itself repeatedly. In Half-Blood Prince, Hermione quotes an article in The Daily Prophet which stated that "the entire stock of Ministry Time-Turners" was destroyed during that incident. The books do not discuss who else may be in possession of Time-Turners outside of the Ministry. Time-Turners are very dangerous when in the wrong hands, as it's said that many wizards met their demise after confronting and accidentally killing their own selves from the future so they are issued very carefully.
Hermione's Time-Turner resembles a gold hourglass pendant on a necklace; it is unclear if all of them do. The user twists the hourglass pendant, with the number of twists corresponding to the number of hours of back travel required. Read more on Wikpedia.org HERE.