With the vector module, you can draw new arrows and modify or delete existing arrows.
To draw a new arrow, you must be in vector mode. You can enter this mode by clicking the purple arrow from the Tools menu that appears when you click on the diagram (you may need to scroll down to see the entire menu). The first time you click on the diagram, you will be in vector mode by default.
In this mode, you can click and drag to draw new arrows. Each time you click and hold, a new arrow will be started from that location.
Once an arrow is drawn, you cannot modify it while in vector mode.
To modify an arrow you have already drawn, you must be in select mode. You can enter this mode by clicking the black arrow from the Tools menu. If you click outside the diagram, and then click again on the diagram, you will be placed in select mode by default.
In this mode, you can modify already-drawn arrows by dragging their endpoints. You can also drag an entire arrow without changing its length or orientation. To remove an arrow, click on it somewhere between its endpoints to select it, and then press the delete key on your keyboard.
You cannot draw new arrows while in select mode.