"He is credited with..." means "people give him credit for..." For example: "Ronald Reagan is credited with helping to bring down the Berlin Wall." means "People generally agree that Ronald Reagan helped bring down the Berlin Wall." "Revolutionizing" means bringing about a revolution/change. "Bikes revolutionized transportation by allowing people a cheap, fun, and healthy way of covering large distances." "auction houses" are companies that run auctions. Auctions are sales where an item is sold in front of a group of people. Someone will say "I'll pay $10 for this." Then another person might say "I'll pay $20." It continues until no one wants to go higher. The person willing to pay the most can buy the item. "by pioneering..." means "by being the first people to...". It originally refers to people who are the first to settle a region of land. "such sales as the jewels of the Duchess of Windsor and the Jacqueline Kennedy Onassis estate" simply refers to sales of rare and valuable items. "in the 1980s and 1990s." refers to the time period.