The Outline view pane is a handy way to navigate within, or select a specific component of, a design element such as a custom control. Its default location is the bottom left of your Designer window.
A control is a design element provided by Domino Designer. A control can help with data or layout. Controls can be dragged and dropped from palettes, which speeds up XPages development. By default, the palettes appear on the right side in designer when an XPage or control is open.
An XPage is the main container design element that displays to the user.
A custom control is similar to a subform, but it is much more powerful and flexible. It is built by the developer, and can contain one or more other controls, including other custom controls. All custom controls in an application are available in their own palette.
A repeat control is one of the more useful controls. As the name implies, it repeats whatever is inside it (usually a list or array) the designated number of times. It can contain one or more other controls, including other repeat controls.