The selection mode is the default operation mode which corresponds to the Arrow tool 
. You can adopt it again at any moment by selecting the tool or by clicking with the right button of the mouse.
Selecting a graphical object
A click on an object (or on a link) allows you to select it; small square marks (handles) appear on the corners and the sides of the object and indicate that it is selected.
A double-click opens a dialog box.
This dialog box displays the description of the object (or of the link) and can be used, either for creation (the fields are then blank), or modification, or just display, depending on the circumstances.
Single selection
A single click performs a single selection, i.e. all the objects previously selected (identified by small square marks) are not selected anymore.
Extended selection
You can select several objects by pressing the Ctrl key while clicking on the objects.
Rectangle selection
You can also select all the objects located in a given work space area by clicking with the right mouse button on the background of the work space and dragging the mouse while holding the left button. A rectangle is drawn until you release the button: all the objects entirely contained in the defined area are then selected simultaneously.
Full selection
The Select all option of the Edit menu option selects all the objects simultaneously.
Deselection
Click the background of the model (outside any object) to deselect all objects.