The Anchor function will allow the insertion of a link into your UI. Most web pages have links to go elsewhere, and this is how you add a link in GS:

function Anchor() {
  var mydoc = SpreadsheetApp.getActiveSpreadsheet();
  var app = UiApp.createApplication().setTitle('Anchor'); 
  var mainPanel = app.createVerticalPanel().setId('mainPanel');
  app.add(mainPanel);
  
  var googleLink = app.createAnchor('Google', 'http://google.com');
  app.add(googleLink);
  
  mydoc.show(app);  
}