Beginner here need advice on glass

[soldier-of-the-apocalypse]

The third knob I think you're looking at the parallax adjustment.

Here's a good overview on Mils and one on MOA

Mils and MOA are just two ways of measuring angles. Neither one is better than the other, but to keep your life simple it would be smart to go Mil/Mil or MOA/MOA.

thanks that helped a lot I prefer the moa system