How did the Vikings settle in Briton?

Viking settlement of Britain followed many years of sustained raids on British monasteries in the eighth and ninth centuries. As centers of relative wealth, these monasteries were natural targets for the Vikings, who were raiding elsewhere throughout Europe at the same time. Over time, many of these brief and bloody raids turned into settlements. This was never really a deliberate process in the same way that Europeans colonized the Americas, but bands of Vikings simply remained in the areas they had invaded. These were especially concentrated in northern Britain, where their presence contributed to the creation of the kingdom of Scotland. They also settled in Northumberland and East Anglia, which they used as a sort of base for the conquest of the kingdoms of Wessex and Mercia.   Invasions by Norsemen continued well into the eleventh century, when Harald Hardrada led an attack that coincided with that of William of Normandy. By that time, Viking settlers had long since been incorporated into British culture. 
http://www.bbc.co.uk/history/ancient/vikings/overview_vikings_01.shtml