In the Instructor's Page of your custom course, you can see your students' progress in the Student Progress tab. Select a chapter/unit from the drop down menu to see your class' progress on that chapter and all the exercises in it. You can click on each student or each exercise to see the details. There are also two buttons for Chapter Activity (which used to be called Overview Reports) and the Gradebook.
The Chapter Activity (video tutorial) provides a spreadsheet with each student and how many exercises they have attempted on each page/lesson. This is a quick way to see what they have attempted and completed. However, they are not graded. The coding exercises can only be manually graded at this point. The spreadsheet has filtering functions built in with the down triangles on each column and can be downloaded to use in Excel or Google Sheets.
The gradebook is for assignments that you have given and graded (see Creating and Grading Assignments).
Chapter Activity spreadsheet