Here's a little tutorial on how to cluster WebSphere application servers. It's an earlier version of WebSphere, but the concepts haven't changed, so you'll get the right idea.
How to Configure a Clustered Application Environment for the WebSphere Application Server
Basically, you create a cluster, and add 'servers' to the cluster. A 'server' is essentially a JVM. Then you deploy your apps to the cluster, and WebSphere takes care of the rest. WebSphere really is something else, isn't it?