During the reservation steps and on your summary pages, you'll see that there is a a side bar with icons displayed on the right hand side. Here we'll list useful tools you can reference, simply click on an icon to open the full list.
'Document Store' is where you'll be able to view and download all files added during the purchase. This will be split out by type but you also have the ability to download them all in bulk too by clicking 'Download All'. You'll also have access to a Shared Store, where you can upload files for the seller to view and download and similarly download files they upload also.