Star

A star was a ball of gas composed of hydrogen and helium. Stars existed throughout the universe and often were orbited by planets.

By the pattern of the stars in a sky, one could determine one's time zone. (TV: Heaven Sent) On Skaro, the First Doctor hoped to fix their position by the stars. (TV: "The Dead Planet")

Composition
In the pre-universe, stars were doughnut-shaped. (PROSE: Millennial Rites) When the universe was rationalised they became spherical. (TV: The End of the World, 42, Amy's Choice, The Rings of Akhaten) In the after-universe, the stars were spherical, but usually green. (COMIC: The Stockbridge Child)

Stars gave off a wide range of radiation, including ultraviolet light, visible light and more dangerous radiation. (PROSE: The Sons of the Crab)

Stars of sufficiently large size would destroy themselves in a supernova. (TV: The Pandorica Opens)

Manipulation
In general, only more advanced species were capable of manipulating or using stars.

The Time Lords were capable of controlling stars to their own ends. They used stellar manipulators like the Hand of Omega to control stars. (TV: Remembrance of the Daleks) The Tenth Doctor said they invented black holes. (TV: The Satan Pit) They used the black holes to power their time travel. (TV: The Three Doctors, The Deadly Assassin)

The Great Old Ones could be returned to their bodies by the positions of the stars. Unfortunately for them, the constant expansion of the universe meant the stars would never return to their proper positions. (PROSE: White Darkness)

The early Chronovore fed on stars. (PROSE: The Dark Path)

The Osiran GodEngine was capable of destroying a star. (PROSE: GodEngine)

Artificial stars
Some time before 905 BC, aliens created artificial stars which formed into a living constellation called the Gryphon. (COMIC: In the Stars)

The Company used in-station fusion satellites to create six artificial stars for Pluto. (TV: The Sun Makers)

The Aapex Corporation created artificial stars for Nooma which also functioned as starships. By the time the Third Doctor visited the planet, only one of them was still functioning. Juliu Epreto wanted to take control of it and use it to depart his world, but the Doctor prevented him from doing so. (PROSE: Speed of Flight)

Other references
The reality bomb caused the destruction of all reality, making the stars seem to "go out". (TV: Turn Left, Journey's End) The total event collapse, the destruction of the universe, caused every star to supernova. (TV: The Pandorica Opens) The stars went out when the Great Intelligence invaded the Doctor's time stream to turn all of his victories into defeats; this was witnessed by Madame Vastra on Trenzalore. (TV: The Name of the Doctor)

Torajii was a living star. (TV: 42)