After an assessment, there are three views of the same data, and they answer different questions.
Getting there
Open the classroom, go to Assignments, click the assignment and then the lesson.
Students: how did each person do
One row per student with their total. Click a name to open their submission on the full-screen review screen, with every answer, mark and piece of feedback. Bulk actions across the top cover CSV export, resubmission, marking as completed and returning work.
Blocks: how did the class do on each question
One row per question, with the average mark. Click one to open the review screen on that question, with everybody's answer side by side and a Summary that charts the spread (a Marks Distribution for long answers). Sort the answers by marks to find the strongest and weakest. This is the view that finds a misconception. See Moderating one question across the class.
Insights: what should I reteach
The Insights tab pulls out the themes across the class, so you do not have to infer them from thirty scripts.
For usage across the whole school rather than one assessment, use Insights in the sidebar. See Organisation Insights: where to find them and what they mean.