When you use the Resources tool to upload an item, you can choose to keep that item accessible only to members of your site, or you can choose to display the item to anyone who can log into the system. The latter option also allows you to share an item with the participants of another site.
To allow people outside your site to see your resource item, you
must change the "Access" parameter to
Display to non-members
(publicly viewable). You can do this in Resources while you're
uploading an item, or later, after it's uploaded. For more
information, see Creating/adding, editing, or deleting a resource item.