Scenario 1: Extenuating Circumstances
If you have serious extenuating circumstances like a medical condition or family crisis, definitely explain them on your application. This would fit in the “extra information” box for sure, but it could also be good material for your personal statement.
For example, if you have a low GPA because your family had financial troubles, both of your parents started working long hours, and you became the primary caretaker for younger siblings and didn’t have time for homework, that should definitely be on your application as part of your story.
Or if your grades suffered due to a medical condition, you should definitely make that known on your application.
In short, if you had serious outside circumstances that affected your grades, make sure you explain them thoroughly on your application. You want to make sure colleges know that, in your case, your GPA wasn’t entirely in your control.
You should highlight academic interests and classes you did do well in, but the explanation of your circumstances will be the best way to help admissions officers evaluate your file fairly.