A positive statement is objective and therefore can be scientifically tested for legitimacy based on available evidence. An example is, "Driving fuel efficient cars leads to less road rage." A normative statement is opinion-based and subjective. An example of this: "Gas prices are unfair."
Positive statements focus around what is; normative statements focus around what could be. Normative statements carry value judgments intended to persuade listeners or readers. Similar to the purpose of a hypothesis, positive statements are proven or disproved following test results. Economists make a distinction between positive and normative statements as a way to establish open communication between people with varying views.
Positive statements aren't always fact. They can be wrong but must be testable. It is impossible to disprove a normative statement because it's based off another's opinion.