The Mux allows you to handle multiple network connections at once, including to the web server.
The xPico Wi-Fi User Guide has the full command reference on Chapter 16. Please refer to that document for all the available commands.
The Forums has several examples on how to use the Mux. For example, to dynamically update data on a webpage on the xPico Wi-Fi's webserver, see this post: http://forums.lantronix.com/showthread.php?t=1032.