Centrally, the Battle of Hastings, when William the Conqueror defeated the English King Harold. However, the story in the tapesty starts years before, and gives the reasons for the invasion. It's the first recorded historical strip cartoon.
By the way, it isn't really a tapestry, which is something that is woven. It's an embroidery. Worth a visit to Bayeux, but I'm sure a good Googling will give you lots more.
Adieu.