For an intro on JMX, have a look at https://blogs.oracle.com/jmxetc/entry/what_is_jmx
The jmx-console in previous AS versions was a web-based browser for the exposed JMX beans, nowadays you can use JConsole etc (https://community.jboss.org/wiki/UsingJconsoleToConnectToJMXOnAS7) for viewing the information. Is there anything specific you are looking for?
Thank you Nicklas. Actually, I am trying to monitor the DB connection pool. I am using jboss-as-7.1.0.CR1b. I am able to see the pool usage by http://localhost:9990/console/App.html#ds-metrics. Is there any other way to view the connection pool status?
There is the CLI and the http/REST interfaces etc but they pretty much all lead to the same place.