How's that confusing?!
They say enter your information exactly as it appears on your transcripts. Don't get creative adding spaces or using lowercase, when you need to use uppercase letters. Go to your admissions and records office and request an unofficial copy of your transcripts, put it in front of you, and enter exactly what you see on that piece of paper. The same thing will be mailed out to AADSAS. So, if you do so, there's no chance they'll find any discrepancy between what you entered and what appears on your transcript, which means your application will be fine. I did the same thing and my application was mailed out on 6/29 without any problems whatsoever!
There's a course description (Example: INTRO TO CHEMISTRY) and then there's a course number and a departmental prefix which go together (Example: CHEM 12). When they say enter exactly what you see, you can't decide to drop the "CHEM" and only enter the "12." It's really not that hard to comprehend.