Forgive the delay, but I just noticed this request. When you click on the symmetry you must also select an axis for the tool to create the symmetrical object.
Two days ago I discussed this very question with another person and they couldn't get the tool to work on the object they were creating. I had them send me the Hex file and sure enough, the tool just wouldn't work on that object. It worked on other objects I created but not on hers. I just couldn't fix it and she had to create the model all over again. This is probably a problem with the program and not the method as the method/technique isn't broken, just the tool acts finicky.