On Pivory.com there's a new topic (tutorial) showing you a simple example of using WebSockets with the Ratchet PHP library, complete with sample code.

WebSocket is the modern way for realtime two-way communications between server and browser. In the beginning we have Ajax calls [...] and with WS in picture the logic becomes [different]. [There] is a separate WS server, say listening on xxx.xxx.xxx.xxx:8080, and it can send messages to connected clients in realtime at any moment. The WS server can be in any language (such as node.js + socket.io) and on any machine or even in a cloud service. I use PHP (try http://socketo.me for Ratchet) because I am lazy.

The example shows a basic PHP Web Socket server running on a port with methods for "on connect", "on close", "on error" and "on message send". There's an example of the Javascript code to connect to this socket, showing how to convert it over from Ajax usage.