All measurement features are located under mainmenu/utilities/measurement. Some of these tools will measure only selected shapes.
Manual or automatic ruler can be used. For a manual ruler click two points with the mouse. To make the ruler permanent hold the control key on the second click. For an automatic measurement in x and y-direction to the next edge of a visible shape hold down the shift key on the first click. Also here you can make the ruler permanent with pressing the control key. A permanent ruler means, that the rule is added to the acitve layer. With a shift+control key on the first click you can delete all rulers.
An angle between two or three entered points is measured. In case two points were enter the angle will be calculated to the x-axis. When three point are entered the angle is measured between these three points with the first entered point as center.