If you're enrolled as a free audit learner, you won't have access to graded assignments and exams. You can expect to see a message encouraging you to upgrade to the verified track on any page that features a graded assignment.
Comparison: Verified vs Audit track
| What's included? | Verified Track | Audit Track |
| Verified Certificates | yes | no |
| Graded Assessments and Exams | yes | no |
| Discussion forums | yes | yes |
| Videos | yes | yes |
| Readings | yes | yes |
| Practice (Ungraded) Assessments | yes | yes |
You can read more about the difference between the free and paid experiences here.