Introduction - If you have any usage issues, please Google them yourself
The definition of Ajax (Asynchronous JavaScript + XML)
The presentation of XHTML+CSS based on standards-based presentation;
Dynamic display and interaction using the DOM (Document Object Model);
Data exchange and related operations using XML and XSLT;
Asynchronous data query and retrieval using XMLHttpRequest;
Use JavaScript to bind everything together. See the original article from Jesse James Garrett of Ajax.
Similar to DHTML or LAMP, AJAX is not a single technique, but an organic use of a series of related technologies. In fact, some ajax-based "derived/composite" technologies are emerging, such as "AFLAX". Include source code.