If you have received a Document Request notification from you customer, you need to upload and share the relevant document against the request.
You can access your request by either clicking on your task or navigating there via the Supplier Approval Tab - Document Request manager - Received Document Requests:
Find your request and click the blue plus
Select your document and Save. The document status will turn Grey and tell you the file was successfully uploaded.
Repeat these steps for each of the documents which have been requested.