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 early Gallifreyan 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 so they could gain the same power over time as the Time Lords. He programmed the Hand of Omega (TV: Remembrance of the Daleks) to detonate Skaro's second sun, (PROSE: The Stranger) sending it supernova and vaporising Skaro. (TV: Remembrance of the Daleks) One account claimed that the Hand of Omega made Antalin's star go supernova and vaporise the planet instead of Skaro. (PROSE: War 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 universe itself was rebooted. (TV: The Pandorica Opens)