So we’re talking about two different things.
Using the reticle to range a target means to find a target at an unknown range and calculate its range via your hash marks.
The next step is using your reticle to then adjust your point of aim to allow for the drop of your round.
If you’re using a factory known value ammo you can just plug those numbers into a ballistic calculator and run with them. To be more accurate pick your specific load and chrono them.
For example
View attachment 66470
So with that given load, at that given elevation, at that given temperature, and at a 0 angle if your target was 400 yards away you’d need 6.17 MOA of elevation to hit the target. You can either dial up your elevation turret 6-6.25 MOA or hold above your target 6.25 MOA. (On your reticle basically 3 hash marks).
using the reticle to determine the range of the target isn’t super accurate, although you can get fairly good with practice. Most people either shoot at a known range, close enough the bullet drop doesn’t matter, or carry a laser rangefinder.
Deciding to either dial up your MOA or hold above with your reticle can depend on the size of the target, the range you’re trying to shooot at, how expediently you need to make the shot.