Simply put, CLASSPATH is a variable that contains a directory, like this:
# Linux /opt/jars # Windows C:\jars
Typically, JARs are located in the CLASSPATH directory. A Java application uses CLASSPATH to know what directory contains the JARs.
# Linux /opt/jars/example.jar # Windows C:\jars\example.jar
On Linux, this command will temporarily update the CLASSPATH variable to contain a certain directory.
The echo command can be used to verify that CLASSPATH now contains /opt/jars.