In order to assign fee type to grade, please follow the steps mentioned below,: 

- Go to Fee Management > Fee Types > Fee Types.
- Click on Actions button (down arrow).
- Click on "Assign Fee Type to Grade(s) or Student(s)".

- Click on Grades. 
- Search for Grade name and select the required record.
- Click on Save button.

-Tuition Fee is assigned to the selected Grade. 

You can also refer to article How to assign fee type to student for details.

Note: When a fee type is assigned to a grade, then for all the enrolled students in the grade, if any student has an open & unpaid invoice, then assigned fee type is added to the invoice. Otherwise, a new invoice will be generated.