Lists allow you to divide your board into different categories that are either time- or event-based. Typically, a list represents the stage of progress ("to-do", "in progress", and "done") within your project.
Lists are great for setting up different buckets to organize your tasks, notes, or content. Lists are made up of cards, or the Notes, Tasks, and Content that make up a specific stage of your project. Lists can be moved - drag-and-drop is the more exact term - anywhere on your Board. You can even move all cards in a list to another Board, essentially replicating the activities on that List in another project.