Attachments option allows to add and download additional files to the design selected. Users with permissions to edit and/or export designs will have this option available. Once the option is enabled in Administration, you will see a new button 'Attachments' available on the bottom menu.
Select one design and click on the button 'Attachments' and choose 'Add Attachment...'
In the new dialog upload the attachment (single file upload only).
Once uploaded the file is attached and you or others with permissions will be able to download it. Clicking on the file icon you will be able to view the attachment.
To view all attachments, click on 'Show Attachments' and it will show all the attachments for the selected design with download option.