Select Angle from the Measurements drop down menu (or press the A key).
Press the left mouse button and drag the mouse to draw the first arm of the angle. Release the button and move the mouse to draw the second arm. Click the left button to finish drawing the angle.
The angle value is displayed in degrees.
You can move the entire angle or one of its endings by dragging it or the cross-marks with the left mouse button pressed.
The label may also be dragged to a more convenient place if necessary.