Parsing

parse vt. To determine the syntactic structure of a sentence or other utterance (close to the standard English meaning). "That was the one I saw you." "I can't parse that.". Jargon File
That is, how to turn an XML document into a data structure you can use.
XML was designed to be easy to parse, so many XML parsers exist. It is unlikely that your favorite language will not already have one.
All parsers implement one of the two well-known API's: SAX and DOM.