Store values of multiple attributes with checkbox in rails db

I have a favorite group model where I have the fields: name, description, grade and subject_areas.

I want both grade and subject_areas have multiple values. In the form for creating the favorite group I want to implement these two fields using checkboxes.

I know it is possible, but I am unable to find any proper answer for multiple fields having checkboxes. Maximum questions I have searched in this forum has been done for single field with checkboxes. As I am new to Rails I am unable to find a proper way. And also the values are not getting stored in the database. Please suggest a way. Thanks.