If you are using a merged course that combines multiple sections into a single course, or if you have created groups in your course manually (see Organizing users into Moodle Groups), it is possible to view the gradebook by individual sections (e.g., you want to view or edit grades for students in section 02 only). To filter by group within the gradebook, you must first enable group mode within your course settings.
You should be aware that whichever group mode you select for your course will become the default group mode for any newly-created activities (e.g., assignments, forums, etc.) moving forward (but note, existing activities will remain in whatever setting they had prior to setting a new default). Here are the differences between the two options:
As an example, in a forum set to Separate groups, a student would only see and be able to reply to postings from other members in the same group, but when set to Visible groups, the student could see all postings from other students in the class but could only reply to posts from other members in the same group.
Since this change only affects group settings for activities created after making the choice, any existing activities will remain set to the original course default, which is generally No groups (everyone can see and interact with anyone else’s activity regardless of group). As such, you might consider creating all course activities first before you change the default setting, or else you will need to change the default each time you create a new activity, unless you do indeed wish to limit interaction within the activity by groups.