i want to build a form that can be used for entering grades of various subjects at a school
Welcome to the ODK forum, @GomezganiMsowoya! We're glad you're here. When you get a chance, please introduce yourself on this forum thread. I'd also encourage you to add a picture as your avatar because it helps build community!
Building that type of form is possible! The ODK documentation is a great place to start to learn about the different features and functionalities: https://docs.getodk.org/
This page - https://docs.getodk.org/xlsform-first-form/ - has a video tutorial on building your first form.
If you have specific problems or issues while creating your form, the forum is a great place to ask questions.