Greetings,
that's a bit generic and you will need to provide many more details please:
1) How to you start the H2 server (e.g. java -jar libs/h2.jar from the console)
2) What is the output on the console after starting it
3) How do you connect to the H2 server (e.g. URL connection settings)
4) What network ports are in use and does your firewall allow for them
Good luck and cheers
Andreas