Hi Andrea,
I'm not exactly sure what you're asking for, but you can add a URL to a collection description in DSpace (which could be followed to reach another DSpace collection or any external website). On the Edit Community or Edit Collection page, in the Introductory Text (HTML) box, you can add HTML including links. The structure for links is:
<a href="Your URL Here">Your Link Text Here</a>
If this isn't what you're looking for, please respond to the group with more details about your question.
Laura