I didn't put anything in the additional coursework section. I think it may be left over from before they took the regular course history section out (i got an email about this: "In response to concerns about the Course History Section within the P&S Secondary Application, this section has been removed from our application. If you were already in the process of filling out your application, you will no longer see this page. When you print out your copy of the completed application, you may see this section, but in a blank format.")
I think they left that page in so that you could still upload documents if you had weird stuff about your educational history to explain. the columbia secondary is really badly mismanaged. i had all sorts of problems with my application when i was previewing the completed app.... questions on the preview that didn't exist in the online app so you couldn't answer them, etc. when i called to ask about them, i got told very curtly that none of it mattered. so, whatever. i did my best and submitted it.