Sight Alignment vs. Sight Picture
Sight Alignment is the process of lining your sights up for both vertical and horizontal equilibrium. Looking at the picture below, we see that the front sight post is lined up perfectly vertical with the rear sight, which indicates that the muzzle is pointed straight ahead. This ensures that the elevation (the "up and down" motion) of our Point of Impact will be correct.
Next, you will note that the distance on both sides of the front sides is equally spaced in correlation to the rear sight. This is how we can ensure that the Point of Impact will not miss to the left or right of where we intend.
In short, the red lines in the image below should be the "mental test" that the shooter takes before each shot. The top of the front sight post should line up in a perfectly straight line with the top of the rear sight post, and the space on the sides of the front post should be equally spaced on the left and right. This will ensure that the Point of Impact from our bullet can be reasonably controlled and predicted when accompanied by proper Sight Picture.
Sight Picture is the joining of the Sight Alignment with the target in the intended area that we are trying to hit. In other words, it's how we join together our "Point of Aim" with our "Point of Impact" with consistent, repeatable results. The picture below demonstrates how the proper sight alignment should be placed over the target, thus giving us a good Shot Picture.
Assuming that our firearm is properly zeroed, our hits on target should be directly in the center of the bull's eye.
Once the proper Sight Alignment and Sight Picture are acquired, a smooth and steady trigger pull will allow us to break the shot without a disturbance in our Sight Picture. This will allow us to consistently control the relationship between our Point of Aim and Point of Impact.