ImportXML lets you get information from filetypes such as xml, html, csv, tsv, as well as RSS and Atom feeds that you might read today in Google Reader. It can only read publicly available files by default. Data in other spreadsheets can only be referenced after the relevant spreadsheet has been published.
URL is the URL of the XML or HTML file. Query is the XPath query to run on the data given at the URL. Each result from the XPath query is placed in its own row of the spreadsheet. For more information about XPath, please visit http://www.w3schools.com/xpath/.
Example: =importXml("http://www.toysrus.com"; "//a/@href"). This returns all of the href attributes (the link URLs) in all the <a> tags on http://www.toysrus.com homepage.
Note: The limit on the number of ImportXML functions per spreadsheet is 50.