Right click on the Google Maps display window at the location of the start of
your distance measurement.

Click Measure distance.

Click the end of the distance measurement.

To move the end or start of the distance measurement drag of the circles at the
ends of the ruler.

To inert an additional point, drag the ruler from a point between the two ends.

Or click a new end past the last end.

To clear the measurement right click the Google maps display window and click
Clear measurement. Or just click on the end of the ruler to remove that point or
the whole ruler if only two points.

Play with it to learn about it.