Though piracy has been around since the 14th century BCE, the rise of the Atlantic pirates (which are the ones you are interested about) can be pinpointed to two events. The first event which allowed for the rise of piracy in the Atlantic was the English use of privateers to harass Spanish trade in the new world. England was a small and relatively weak country at the beginning of Queen Elizabeth's reign. Spain and Portugal had an early start in extracting wealth from the new world, and England was afraid that it would be left out of the frenzied scramble for colonies. In an attempt to break the Spanish monopoly on the new world, Elizabeth pushed for the creation of colonies far from the traditional Spanish footholds, while at the same time allowed English privateers to prey on Spanish vessels in an attempt to weaken Spain's hold on the trade from the new world. By legally sanctioning piracy, Queen Elizabeth was allowed to slowly chip away at Spanish dominance in the new world, and increase British influence in the Atlantic. And they did this with relatively small expense as they didn't need a standing army or naval presence in the region.

The second event which allowed for the rise of piracy in the Americas was, as Captain Charles Johnson wrote in one of the few "reputable" primary sources of pirates, "the great Commerce thither by French, Spaniards, Dutch, and especially English Ships." (Johnson, 30) Following the decline of Spain's monopoly over the colonies of the new world, the once legal privateers of England shucked the yoke of their country and became pirates. The mass of wealth traveling across the Atlantic was too much of a temptation for sailors who, due to the poor conditions on many of the merchant ships, became "desperate, [and] turn'd Pyrates, robbing not the Spaniards only, but their own Countrymen, and any Nation they could lay their Hands on." (Johnson, 30) The former privateers were able to find willing and able crewmen in the various sailors on merchant ships sailing throughout the Atlantic. The merchants of England (and other nations) often cheated many of their sailors out of food and drinks, paid relatively low wages, and allowed deplorable conditions on their ships. This created a belief that the horrors of ocean life were so great that the sailors might as well rob and pillage and enjoy themselves while possible as their lives were relatively cheap and short.

The reason for the treatment of sailors as cheap and expendable, is because sailors were relatively cheap and expendable. The rise of piracy coincided with the disruptive influence capitalism had on traditional economics. The peasant agrarian class was slowly being squeezed out of existence with the decline of agrarian economics, and they were forced to move to the large cities of England and become employed wherever they could find work. This led to many individuals shipping out as sailors on merchants ships. The relatively abundant labor offered by these poor peasants allowed the merchants to skimp on necessities, which in turn led to numerous mutinies by sailors who would become pirates and prey on the shipping lanes of the new world.

One of the best books written about pirates is Villains of All Nations by Marcus Rediker. In it he claims that "impressment, beatings, poor food, and the disabling and deadly effects of these on themselves and their families" was one of the central reasons for Atlantic sailors to turn pirate. It was the "thirst, hunger, wounds from lashings, and premature death that these helped to engender were central to deep-sea faring in this period, and even more central to the decision to go 'upon the account'". (Rediker, 57)

So, in short, you had some privateers who had their own ships and were legally allowed to attack Spanish shipping in the Atlantic. Once the war was over, they wanted to continue to take prizes and decided to attack all merchant ships in the Atlantic. And you also had merchant ships which would be taken over by disgruntled sailors. Pirates who would seize a merchant ship would also allow the sailors from that ship to 'go upon the account' (join the crew) and this would increase the size of the pirate crew."

Charles Johnson "A General History of the Robberies and Murders of the most notorious Pyrates".

Marcus Rediker "Villains of All Nations: Atlantic Pirates in the Golden Age"

Also where did many get their nautical skills? Did many start out in a navy or as fishermen/merchants?