The Property Editor is the main panel that you use to design each page's different elements, and customize events and actions. It is a draggable popup that will show the different fields that can/should be filled for an element, action, or event. It appears when you double-click on an element, or click once on an event or action. The top bar lets you rename the element/action/event you're editing, and the icons on the right let you show the Element Inspector, the Comment Panel, or some contextual videos.