XML is a text-based markup language so any simple text-editor like Notepad is enough to create and edit XML documents however if you need to create complex XML documents quickly and easily without errors then what you need is a XML-specific editor. These XML editors comes with fine features like a graphical user interface and different graphical views of your XML document, syntax highlighting, structure checking, schema validation and create XSLT transformations.
Some of the popular XML editors are
As you have already seen now, XML is text based and XML files can be opened with XML editors or text-editors. But it is not just the XML editors and text editors, web browser can also display the XML. You can open the XML file in your browser just as you would open an html page. By default most of the major web browsers display XML elements in an expanding and collapsing tree structure. To change this default presentation you can use a stylesheet that specifies how the XML document should be displayed.
This is how an XML file will be displayed on Internet Explorer