There are two ways to link file submissions on the submission page.

The Add a File option will allow you to add a file that already exists in the system. Either from your portfolio or a file locker that you have access to. 

To upload a file from your computer, click the "click" option in the Drop files box. This will open a navigation pop-up so you can find and select the file you want to submit. 

Once you have selected to file you want to upload. Click open. Add any additional comments and click Submit.