Your standardized score(ACT/SAT) and classroom GPA are on a sliding scale. If you have a high GPA, your "score" could be on the lower side. If you"score" is high you GPA can be on the lower side, say a 2.5, but your "score" better be around 1100 or so.
I don't know exact numbers, there might be a website.
It's not something that can be explained easily. You would need someone in the admissions office to explain how it works. Each school has certain GPA, ACT/SAT scores to qualify. You also have to have certain coursework finished in high school like Algebra, Physics, Chemistry..etc (not sure on which topics exactly)
Nebraska, as well as all of the other big twelve schools, are towards the lower end as far as scores needed to qualify. I believe that they are around a 900 and a 2.4 needed, or a 1150 and a 2.2 needed, which is pretty low for most colleges, but there are lower.