The Marks card is a key element for visual analysis in Tableau. As you drag fields to different properties in the Marks card, you add context and detail to the marks in the view. You use the Marks card to set the mark type (see Change the Type of Mark in the View), and to encode your data with color, size, shape, text, and detail.
Three separate fields have been dragged to different attributes in the Marks card in this example. Color is associated with segmentation, region with shape, and quantity with size. After you’ve added a field to the Marks card, you may alter the property it uses by clicking the icon next to it. You can also adjust those settings by clicking the property buttons on the Marks card.