Step 1
Go to Configuration -> Grades and add the grades you offer. Example: Toddlers, preschool, grade R, etc.
Click the + to add a new row

Type the name of the grade into the blank field in the Grade column, and click the Save button to save the changes.

Repeat for each grade.
Step 2
Go to Configuration->Classes and add the classes. If you have more than one class for a grade, you need to add each class and link it to the grade for that class.
Below is the example from the Demo system. Note that Class 1 is the only class for Grade ‘Toddlers’, whereas grade ‘Pre-school’ has 2 classes (Class 2 and Class 3)

The description field is a meaningful name the class. It may be a description, such as 'Toddlers Class 1', a location, such as 'Class 1A', or any name you want to give it.
Step 3
Go to Students -> Students and start adding the students.
In the Enrolment Information section you will be able to select the grade and class you created earlier.