Short answers, pulled from the story.
The confederation of Cinque Ports emerged from the late Anglo-Saxon period specifically during the reign of Edward the Confessor between 1042 and 1066. Certain south-eastern ports received local profits of justice in exchange for providing ships to the Crown.
The original five ports were Hastings New Romney Hythe Dover and Sandwich. In medieval documents Hastings sometimes appears to be given precedence among the ports due to geographical convenience with the ports being conventionally listed in order from west to east.
In return for their ship service the towns received various privileges including exemption from tax and tallage. They held rights of sac and soc which meant jurisdiction over criminal and civil cases within their liberties along with rights of toll team bloodwit fledwit pillory tumbril infangthief outfangthief mundbryce waifs strays flotsam jetsam and ligan.
A Lord Warden of the Cinque Ports was appointed frequently combined with that of Constable of Dover Castle by the end of the 13th century permanently. The joint office survives to the present day but is now purely honorary with an official residence at Walmer Castle.
The continuing decline of the confederation may be ascribed to natural causes such as silting of harbours and withdrawal of the sea. During the South England flood of February 1287 almost destroyed New Romney which became completely blocked by shifting sands while much of Hastings was washed away by the sea in the 13th century.