Social pinning site Pinterest has finally debuted its long-awaited buy button. Users can shop on the site by clicking on “pinned” products to see the price, choose a color, size, and quantity. Visitors can then click on a buy button to complete the transaction using a credit card or by paying with Apple Pay through their iPhones. The new “buyable pins,” introduced Tuesday at an event at Pinterest’s San Francisco office, are a big step by the company to become more of a shopping hub.