XML stands for Extensible Markup Language. We can also say that its text-based markup language is taken from SGML (standard generalized markup language).
We can also call it Markup Language as HTML. XML is designed to store data and you can display that data in web pages. XML also has limitations to store the data.
XML uses tags that are not predefined like HTML tags. You need to use your tag to create and XML. This means, it's more like a self-description. Using the document type definition to represent XML data, it is also called DTD. There is some help. It's also not certain what you really want here, but you can use any text editor to generate XML, provided you understand syntax. The textpad is good, Notepad is free. You can get a free XML Parser with php.