A Class Fee is a group of payment items that allows you attach certain payment  items to a class group or a student. (e.g. a graduating class can have a Class Fee called "graduating class fees" which would include payment items like graduation gown, excursion, graduations party and a graduations ceremony fee) and can be easily add to students the graduating class.

To add Class fees: 
1. Go to setup >>Payment setup >> Class fees
2. Give the Class fee a title 
3. Describe the Class fee (e.g. this Class fees contains payment for graduation gown, excursion, graduations party and a graduations ceremony fee )
4. Select the payment items.