The Edit menu allows you to select and deselect objects. Once objects are selected, they can be operated on using the Objects Library, or Object Line type, color, Object filter settings or Object Point spacing.
This will select all objects in all frames of the scene.
This will select all objects that are in the current frame.
This will deselect all objects in all frames. You may also deselect all objects by clicking the mouse in any blank area of the Viewport.