Like any video game, Call of Duty is an abstraction of real life. While today you may use a laser designator to point out a target to another person, the technology was not there in WWII.

The way that artillery found its targets was through reconnaissance and artillery observers. The area in which artillery was expected to fire was scouted and mapped out ahead of time. Known targets were marked on the maps. For instance, if it was known that there were anti-tank guns in the area, scouts would do their best to estimate which positions the anti-tank guns would take, and artillery would try and suppress the guns before the attack started with a barrage. In the ideal case the guns would be silenced, but things rarely go according to plan and usually there are some stragglers (or worse, the barrage is completely ineffective). In this case it is the job of forward artillery observers to radio the locations of targets to the battery. These observers would also have maps or at the very least be able to report the location of the target relative to some landmark. This required good navigation skills and careful study of the battlefield ahead of some, some guy who grabbed a pair of binoculars would not be able to effectively serve as an artillery observer.