Short answers, pulled from the story.
The Viking force was led by a Norse chieftain named Reginherus, also referred to as Ragnar, who has been tentatively identified with the legendary saga figure Ragnar Lodbrok. He commanded a fleet of 120 ships carrying more than 5,000 warriors up the Seine.
Charles the Bald paid 7,000 French livres of silver and gold, approximately 2,570 kilograms of precious metal, to persuade the Vikings to withdraw from Paris.
The Vikings captured 111 men from one division of the Frankish army and hanged them on an island in the Seine. This was done to honour the Norse god Odin and to break the resolve of the remaining Frankish forces.
A plague broke out in the Viking camp after they occupied Paris. On the advice of a Christian prisoner, the Norse undertook a fast, and the plague subsided. Ragnar later attributed the illness to the power of Saint Germain of Paris.
The 845 ransom was the first of 13 total payments the Franks made to Viking raiders, though the term danegeld was not expressly recorded as being in use at the time of the original payment.
Unlike the 845 siege, which ended with a ransom payment, the city's walls held against the Vikings' greatest attacking force during the 885-886 siege of Paris, marking a turning point in the history of France.