Well, we need to clear up a terminology issue first and foremost. The word "viking" is, in all likelihood, derived from an Old Norse word meaning to go sea raiding. So, in the strictest sense, a viking was a pirate, a raider, a looter and a slave taker. But not everyone, or even a majority, of the Scandinavian population got up to that, and their activities weren't particularly unique except in the degree of success they achieved and the cultural impact imparted on Christian Europe.

Most Scandinavians of the Viking Age were farmers, as in the rest of the world, or fishermen, or foresters, or smiths. They had families and settled lives. Though a minority, society was dominated by landowning males, with comparatively less social stratification than in continental Europe; the gap between petty king, aristocrat, and common freeman was, during this period, less broad. These were the men who made up the raiding parties and the trading expeditions, both of which involved going over the seas to the raiding grounds of England, France, and Germany, or down the rivers of Russia to the trading hubs of Constantinople and Baghdad. There's a link between the two, as slaves taken in Europe could be sold in the Middle East.