After JBoss has succesfully started you can locate the JMX console at http://localhost:8080/jmx-console in the default distribution. Notice that if you have configured the servlet container (Tomcat) to service a different port then you need to supply another port number in the URL.
The JMX console provides a raw view into the microkernel of the JBoss application server. It lists all registered services (MBeans) that are active in the application server and that can be accessed either through the JMX console itself or programmatically from Java code.
Things to do with the JMX Console:
Internationalisation (currently in patch form) - see JBossConsoleI18n
The JMX Console looks like this: