I’m gonna abstract a bit to just help you understand the problem
Create a class called KarateSkill that holds the names of students
arr  //this is an array to hold the student names
Now we have a class that can hold an array of students
Create an instance for Green Belts, Blue Belts, and Black Belts
Boom now we have three instances of our KarateSkills class
One for students of each desired belts
Now I can add methods to my KarateSkills class to do things like add and remove students
Using those methods would look like this
Whenever I don’t understand the instructions of a project or assignment, I re-read the entire problem first. Then build an outline, break it down into very small steps and plan/build one very small step at a time. Eventually things come together. Test things after you’ve coded a small amount and often.
Once you start to get the hang of that, you can think bigger picture things before coding like
“What data structure is best for my KarateSkills class?”
It probably would not be an array in this case. Due to frequent resizing.
You’re on the right track, keep at it!