ECWID is a shopping cart plugin that allows users to add an online store to their website or social media pages like Facebook. The document provides step-by-step instructions for setting up a free ECWID account and creating an online store. This includes adding products, customizing the store layout and settings, integrating the store with a Facebook page, and managing store tabs and pages. The overall purpose is to guide users through setting up their ECWID online store to begin selling products.