Before you can really use your scope, you need to zero it.
When I mount a scope on a rifle, I bore sight it.
To do this, put the rifle in a solid rest where you have at least a 50yd view.
Remove the bolt so you can look down the barrel and see something specific such as a target or perhaps a street sign or the tire of a parked car if you do this at home.
Adjust the position of the rifle so that the object is well centered in the bore and the rifle is stable so it will not move from that position.
Now look through the scope without disturbing the rifle's position.
Adjust your scope knobs until the crosshair is centered on the same object as you have centered in the bore.
Re-check the bore to be sure the barrel is still pointing at the same object and then final check that the crosshair is also adjusted to the same object.
Now you are ready for live fire.
You should be on paper at 50yds so fire 1 round at that distance and make a correction on the scope knobs if you are more than 4 inches off.
Now move out to a 100yd target and fire another round.
You should be within a few inches.
Make your final correction so that when you fire a round, it lands exactly where you were aiming at 100yds.
Now zero your scope knobs.
Every scope manufacturer has a different way of doing this, but most rely on setscrews that you loosen and slip the outer knob, or a center screw that you remove and lift the knob off, then replace in the proper zero orientation.
It does not matter how you do it as long as you end up with the "0" at the proper index park when you are at your 100yd zero setting.
Most scopes have several horizontal index lines to help you find what rotation of the knob you are on.
I recommend taking a black sharpie marker and blacking out all the lower lines, but leave just one line visible below the knob.
This way you will always be able to return to your proper zero position.
Later on, you will build your bullet drop data card from your 100yd zero.
You will record how much additional angle you had to add to get the bullet to hit the aiming point at further distances.
That's why a proper 100yd zero is so important as well as being able to get back to the proper 100yd zero.
It's not uncommon to become "lost in the knob" and lose which rotation you are on.
This put you WAY off your 100yd zero, usually 10" or more at 100yds.