The scope would be “zeroed in” from a bench rest after installation. There are different procedures for various types of scope. But all involve establishing a baseline, or “zero” range. For a normal high powered rfle such as 7.62 NATO it is 100m. Once the scope is aligned at that range, you must establish the trajectory allowances or how much holdover or -under for other ranges. The best scopes are optimised for the rifle and cartridge to be used. Most will have some adjustment for elevation so your are establishing how many “clicks” over or under the zero position correspond to the true distance of the target, Some of the cheapest scopes may lack this and you must actually hold your aiming point over or under depending on range, NOTE: during the initial “sighting in” you also establish your “zero” windage or horizontal setting, which is thereafter only changed based on wind conditions.