The protractor tool lets you measure angles. You can also draw lines at an angle. When tool is active you should see two lines displayed: base line and angle line. You can move the base line's end and middle points to align it with a line or other objects. You can then move the end point of the angle line to measure an angle.
Protractor's angle line has three different modes of operation controlled by the button displayed in its middle point. The default mode is rotation used to measure angles. If you tap the button you can also activate drawing or resizing mode. When in drawing mode, you can draw lines at the current angle by dragging the end of the line. Resizing mode lets you change the length of the line angle without changing its angle.
← How do I use the Protractor tool?