To select multiple objects, simply hold down the Shift key and click on each object you want to select. You should see a selection box surround the objects and can then move them as one group.
Group page elements to duplicate
While you cannot yet duplicate a selection of multiple objects, you can achieve the same functionality by adding a box element to your page and dragging the objects you wish to duplicate into this box. These other elements (text, image, buttons etc.) will become children of the box – which means if you duplicate the box, all of it’s contained elements will be duplicated as well.