You can gather enrollment data by a single term or with a term-by-term comparison.
The default report is enrollment by course, showing enrollment data across all your courses. To see enrollment by term, you will need to change the Enrollment by filter to Terms instead of Courses.
To limit data to a single term or to do a term-by-term comparison, you can select which terms you'd like to show under the Terms filter. Simply check the box next to the particular terms that you would like to appear on the report.