try this link. will teach you the difference between MIl and MOA, and how to use them.
you have practice shooting and engaging target at different distance.
it's pretty close with what you will see through the scope.
The website is foing a pretty good job on getting familiar with tactical shooting and tactical scopes and how to engage targets with taxtical reticle (MOA or MIL)
choose MOA scope because is eazy to do the math without the calculator on field.
Assuming a big Muley buck is 20" back to belly, and he covers 4 minutes in the scope........
20/4 = 5, or 500 yds.
Then minus the 5% and he is 475 yds away.
Very simple, very intuitive and very quick.
He's really 477 yds away, but 475 does the trick.