I opened the site "www.jumpshare.com" but the page opened was only "About us". I did not see any uploaded file and don't know how to see them.

When you open Jumpshare (www.jumpshare.com) the home page opens. (see below)

If you want to see the uploaded files, you need to have the Share Link to the shared folder. You can view and Download all shared files from here.

Or you need to have the link of the individual file shared with you. 

We hope this answers your question. Let us know if the problem persists.