Type in the words you want linked and highlight them. Then click on the button that looks like a paperclip (the "Insert/Edit Link" button). A little box will appear. Add in the complete URL address (including the http:// part) and if you want, make the link open in a new window open. You can also add in a title. This will not appear in any visible location but is used by programs for the visually impaired. Click on "Insert" and there's your link.