Trello is a project management and collaboration tool that allows users to organize tasks, projects, and ideas into boards, lists, and cards. The welcome board provides an overview of Trello's main features, such as adding cards to lists, adding members to boards, labeling cards, commenting on cards, creating checklists within cards, and subscribing to email updates for boards and cards. It demonstrates how to navigate the different parts of Trello to help users get started using the tool to stay organized.