You can insert web links into your prezi by typing (or cutting and pasting) the link, beginning with 'http:' Please note that only URLs beginning with 'http:' will convert to links, and that you cannot substitute other text for the URL address.
Any links will activate after you save and reload your presentation.
Once you have done this, you can open the link when in "show" mode by clicking on it. It will open in a new tab or window. Note that the link will not open when you are in "edit" mode.