If we ignore the additional features, using uWSGI with PHP is somewhat equivalent to using the Process Manager (FPM) that ships with PHP. Just like FPM, the concept is that PHP runs inside a server dedicated to handling the processes/threads running the PHP code. This in contrast to running PHP inside of the actual webserver, like Apache's Mod_PHP, or letting the webserver handle the process management, like lighttpd typically does. In other words, you have the following chain of services: Client -> webserver -> process manager -> PHP interpreter.

He includes some information about the setup ("is it easy?") and how it's more application-based than the usual PHP setup. He also touches on two other larger concerns - is it faster than some of the alternatives and whether or not you should spend time in your day to look into it.