Allegedly? Is it or ain't it?
You've asked a question of a complexity on par with "What is the nature of good and evil?".
For simplicity, and given a scenario of defensive shooting, or hunting of big game, your probably best served setting up the rifle for the "point blank" or "minute of man" (Battle Sight Zero - BZO) sight-in for the maximum distance you expect to engage targets. Use an online ballistics calculator and plug in your acceptable target size (impact diameter), caliber, projectile velocity, projectile ballistic coefficient, and mechanical offset (sight height above bore axis). This will give you the zero distance necessary to enable you to hold the same sight picture for all targets within a given range (no hold over/under) and still impact the target with acceptable accuracy - BZO.
Once zeroed, your point of impact will be below point of aim from the muzzle to your zero distance, above your point of aim between your zero distance and the second crossing of the projectile across your point of aim, and once more below your point of aim beyond that second crossing and falling fast after that. This means that in order to actually hit a target smaller than your selected target size, you must hold over the target between the muzzle and your zero distance, UNDER the target between the zero distance and secondary projectile, and then over the target again for distances beyond the secondary crossing.
You can develop "dope" (observed data specific to your weapon/round) in order to compensate (change your point of aim) for the hold-over/under requirements for a precise point of impact, or simply zero for your rifle/round and hold the same sight picture for all distances knowing your point of impact is within acceptable limits.
If you want a quick and dirty version, zero it at 25 meters and it'll be within "minute of man" out to about 300 meters. Use yards instead of meters if you're a marine
Elementary video explanation:
Ballistics calculator: https://ballisticscalculator.winchester.com/#!/
Understand this is a small fraction of the variables and forces involved, but will get you on your way.
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