You can perform any of the normal edit operations on a set of selected objects, just as you would for a single object, using either the shortcut key or the Edit menu. For example, to Duplicate a set of selected objects, select Edit / Duplicate or press Ctrl+D. A copy of the entire set of objects will be created on your canvas, just below and to the left of the original objects. Note that when you Duplicate or Paste a set of objects, after the operation only the newly-created objects are selected.