Say you are grading an assignment called
Hello World that is out of 20 points.
Using deductive grading, each submission starts out with 20 points. Graders can deduct points to reflect mistakes. By default, codePost assignments will use deductive grading.
Using additive grading, each submission starts out with 0 points. Graders can add points to reflect satisfied assignment requirements. You can use additive mode from an assignment's settings.