The simplest way to test drive the power of ZK is to visit http://www.zkoss.org/zkdemo/userguide.
If you want to run the demo in your local server, you can follow the following steps.
Download zk-demo-3.0.7.zip from here (sourceforge.net).
After uncompressing the file, you can deploy zkdemo.war or zkdemo.ear to your Web or application server.Most Web or application servers have a management console that allows you to deploy an application painlessly. Consult the corresponding manuals, or you can visit http://en.wikibooks.org/wiki/ZK/How-Tos#Installation_and_Configuration, where the ZK community maintains the installation guides for many Web or application servers.For Tomcat server, you can copy it directly to the $TOMCAT_DIR/webapps directory, and then Tomcat will start the deployment automatically.
After zkdemo.war is deployed you can visit it at, say, http://localhost:8080/zkdemo/userguide. The port number depends on how you installed your Web or application servers. Some application servers deploy only the EAR file. That is, you have to deploy zkdemos.ear instead.