Login to Playground on a Chrome or Safari browser. You'll see a dashboard similar to the one seen below. Click on the Paperwork tab on the left hand. Click the File Requests tab.
From the File Requests tab, you'll be able to see uploads your center is requesting. In the Status column, you'll see if you've "Not started", are "In progress", or "Submitted" a form. Click the blue "Complete" button to upload a file request from your computer.
The Upload a document window will appear where you can select the document you'd like to upload from your computer. Once selected, click "Save". You'll be taken back to the File Requests tab where the document will now show "Submitted" and have a submitted date. You can click "View" to see the document you've uploaded.