If you're familiar with iron sights, you'd RAISE the rear sight in order to shoot higher. With a scope, it's not so intuitive.
Follow me here. Let's say your scope is set at the centre of it's elevation range, and mounted on a flat base. If for example your scope has 100 clicks of total elevation adjustment, that would be 50 in each direction from centre; 50 down, and 50 up. You set your rig on a bench, and look through the scope; bingo, the crosshair is dead on at 100. Let's say you previously sighted in at that range, so the bullet hits where the crosshair is.
Now, you set the scope with the offset rings or base so it's pointed downward in relation to the barrel. Remember that you haven't touched your dials at all - yet. When you look through the scope again, you're looking at the ground, or the bottom of the target. Now to get it back on target, you have to raise the barrel of the rifle upwards until the crosshair is on target. If you fire now, the bullet will fly WAY HIGH, because the rifle is pointed up in the air as compared with before you changed the mounts. In order to re-zero the rifle, you have to crank your elevation dial WAY DOWN. In this example, let's pretend you have to come down 30 clicks to get back in the bullseye.
Now you're back to zero at 100, but you have way more clicks available (now 80, rather than 50) in the upward direction before you run out; that extra adjustment range comes from canting the scope with the mount or rings.
Get it? Got it? Good. Go shoot and have fun.