You need to create an anchor to do this.
Select some HTML text or a graphic at the very top of your page then, from the Edit menu, click Anchor and give it a name (i.e. "top").
At the bottom of your page, create a link or graphic that says something relevant (like Top or Back to Top) then open the Hyperlink dialog from the Edit menu. In here, select the page the anchor is on and then select the anchor from the pulldown labeled "Anchor".
Preview the page in a browser to see it working.