Yes. While in the edit mode, highlight the section of text you want to use for the link (the hyperlink), and a little chain link will appear on the tool bar. Click on it, and a box will appear where you can insert the URL you want to link.
If you're linking to your own hub(s), once the hub is in the system, it will automatically drop down in a menu if it is related to the words you're using for the link.
FYI - the site has strict rules about the number of links a hub can have to the same site. No more than two links should go to the same site. Also, a hub can't be overly promotional (filled with text and links to drive business) or used as a teaser that makes people click on a link to get the rest of the information (rather than having informative content in the hub).
Hope this helps! Good luck with your hubs!