The total station (blue instrument on tripod) determines the distance, vertical angle and horizontal angle to the target (yellow prism). That information is sent to the data collector (orange box on tripod). That information may be used for may things, here it was to compute the volume of rock placed. A point (predetermined by some means) may be "staked" (flag set at a position) with this equipment. See YoungSurveying.com to see how calculations can be made on your computer and used with this type of insturment.