A supernova was the detonation of a main sequence star, creating a massive explosion that released incredible amounts of energy.
Omega used his remote stellar manipulator (the Hand of Omega) to send the star Qqaba supernova, thus providing power for the Time Lords' time travel experiments. (TV: The Three Doctors, Remembrance of the Daleks, COMIC: Star Death)
The Seventh Doctor also used the Hand of Omega, programming it and allowing the Imperial Daleks to obtain it. He programmed the Hand of Omega to fly into Skaro's sun, sending it supernova and vaporising Skaro. (TV: Remembrance of the Daleks)
The Eleventh Doctor claimed that he threw his TARDIS Instruction Manual into a supernova because he "disagreed with it". (TV: Amy's Choice) In another occasion, he claimed to have prevented two supernovas. (HOMEVID: Good Night)
The explosion of the Doctor's TARDIS caused every sun to go supernova at every point in history, leaving Earth as the only world in the universe until the timeline was rebooted. (TV: The Pandorica Opens)