CATALINA_HOME is usually the installation directory of
Tomcat.
CLASSPATH is an environment variable used by the Java compiler and interpreter to locate .class files. The value of the CLASSPATH is user defined.
If the CLASSPATH environment variable is not set, then the current directory is used as the CLASSPATH.
However, if the CLASSPATH is set, but does not contain the current directory, then the .class files in the current directory cannot be seen by the compiler and interpreter.
Could you be more specific about your third question?