Frames can be created and used as placeholders (a frame without content) and as graphic elements.
The tools used to create frames are located in the toolbox. Press and hold the Rectangle Frame tool or Rectangle tool to reveal other tools.
The Rectangle tool creates unassigned frames, which contain neither text or graphics to start and can be used for drawing a colored shape, for instance.
A frame size can be changed numerically in the Properties panel.
With a frame selected, you can edit the corner radius by clicking the yellow box in the upper-right of a frame, then dragging a corner. The corner radius can also be edited for a selected shape by choosing Object > Corner Options, setting the options, then clicking OK.