You can see all of the medications that your provider has on file for you on the "My Medications" page. Your current (unexpired) prescriptions are shown first, followed by a list of past/expired medications.
If a prescription is expired or will expire soon, you can request a refill by clicking on the "Request Refill" button to the right of the medication. Doing so will bring up a box where you enter any special instructions, check to indicate that you've read any required notifications from your provider, and click "Submit." The refill request then appears as a pending request awaiting provider review. You can cancel a pending request by clicking "Remove."
Once your provider refills the request, the pending request will disappear and the medication will appear in your medication list.