To add files to the Sandbox​:
 

  1   Access the Documents tab.

  2   In the left navigational panel, under Sandbox, click the Staging Folder.

  3   Navigate to the folder where you'd like to upload a file or files; click the folder to display its contents in the center viewing pane.

  4   In the upper options toolbar, click Add > Upload.

  5   Browse for, or drag and drop items to be uploaded in the Upload Files pane and click Next.

  6   Click Upload.

  7   Click Finish.