In this area, you will find two things here
First and easiest to remember - "Pre-requisites". Some higher level courses require that you take the earlier course. Just like how you might not be able to jump several math levels in High School, neither can you here.
The second and very important is what requirement does this class fulfill. When looking at the public universities in California, there are two systems - CSU and UC. Just like in HS, to get your diploma from a school you have to meet certain requirements. This area will tell you if the class fulfills a CSU course requirement, a UC course requirement, or both (called the IGETC or CAL-GETC) and what area of requirement. Essentially, you don't want to keep taking the same requirement area over and over again as that won't help you with your college diploma as much.