About the markings on the knob and the reticle.
There are two common measurement systems in use on scope knobs as well as some uncommon ones which I will ignore for now.
The most common system is Minutes of Angle, also known as MOA.
The other common system is Milradians, also known as MILS.
Both of these are angular measurments.
One minute of angle is 1/60th of a degree.
Of course there are 360 degrees in a full circle.
So there are 21,600 MOA in a full circle.
One milradian is 1/1000th of a radian and there are 6.283 radians in a full circle.
There are 6,283 MILS in a full circle.
What's important to know is that 1 MOA equates to 1.047" per 100yds and this is commonly rounded to 1" per 100yds.
So, if you are shooting at 100yds, a 1 MOA change is basically 1" on target.
What's important to know about MILS is that 1 MIL is equal to 1/1000th of your distance to target.
So, if you are shooting at 100yds (3600 inches), a 1 mil change is 3.6" on target.
You can convert back and forth between MOA and MILS using the factor of 3.437.
1 MOA = 0.291 MILS or 1 MIL = 3.437 MOA.
I commonly round the factor to 3.5 for easy math in your head.
The following diagram will give you an idea what the angle looks like.
You can see that MILS are much larger units of angle than MOA.
There is another whole thread here that you can read on MOA vs. MILS as it relates to reticles: