You can use rectangles or circles to focus on a specific object on the picture or as a frame for linking in the picture or masking the picture . The functionallity for the rectangle and the circle is the same except for the shape.
Hoover the mouse over the media.
Select the rectangle or circle from the bottom row.
Edit or add functionallity to rectangle or circle
Click and drag the figure to move or resize
Swich between rectangle and circle shape by choosing the symbols to the left