The Vital Sign Framework is layered in the middle of the Java Layered Frameworks, as shown in the Architectural Layer Diagram. Its main purpose is to help you detect problems in your Java virtual machine before it fails. Use it to keep statistics on important events and trend them over time to alert you when you detect a bad trend.
See the Vital Sign Framework Class Diagram for the major classes and methods involved in the framework. The key class is VitalSign, which you extend to create application-specific vital signs. Vital Signs can be configured, like most things in JLF, via property files. See the VitalSignProperties class for information on all the different settings you can configure for each captured vital sign.
The source code for the framework begins here. Here is the JavaDoc for all of JLF, including the configuration framework.