Short answers, pulled from the story.
The novel was ghostwritten by American author Alan Dean Foster but credited to director George Lucas. Foster based it on Lucas's screenplay for the first Star Wars film and later said he didn't mind going uncredited.
Ballantine Books published it on the 12th of November, 1976, six months before the film's theatrical release. Later editions were retitled Star Wars: A New Hope after the film gained that subtitle in 1981.
By February 1977, three months before the film opened, it had sold out its initial print run of 500,000 copies. Ballantine sold another 3.5 million copies over the following three months.
The novelization contains the first reference anywhere to the Emperor's name, Palpatine, in its prologue titled Journal of the Whills. His portrayal there differs somewhat from his later depiction as a Sith Master in the film sequels and prequel trilogy.
In the novelization, Vader actually defeats Kenobi in their lightsaber duel. In the film, Obi-Wan instead allows Vader to strike him down to create a diversion so Luke and his allies can escape.
Later editions of the novelization were republished under altered titles, including Star Wars: A New Hope and Star Wars IV: A New Hope, to reflect the retroactive addition of a subtitle to the film in 1981.