Selection is an important part of editing your images. You can select vectors and pixels (including both at the same time). The current selection can be dragged to move it around and also to move it to a different layer or frame and to copy it to other images. The current selection is outlined and highlighted in blue/green.
The properties of the currently selected vectors can be edited in the Vector Inspector. You can also resize the currently selected vectors by moving their drag areas.
Note: You can only select actual content (ie vectors and pixels). Opacity does not support the concept of selecting empty space in your image.