Once the Geronimo server is running, you can stop it by hitting Ctrl-C in the console window where it's running, or killing the process. Geronimo handles this gracefully, shutting down all the services in an orderly fashion before exiting the VM.

Alternately, you can run the shutdown JAR (using java -jar bin/shutdown.jar) or use the shutdown scripts (bin/shutdown.bat or bin/shutdown.sh) or use the "stop" argument to the geronimo.bat/geronimo.sh script.