java -jar h2-1.3.163.jar -tcp -pg -baseDir /temp/db2
This command line means :
start h2 in server mode, allowing connections only from localhost setting root database to /temp/db2.
Other interesting options are:
-tcpPort 9101
-tcpAllowOthers
-pgAllowOthers
In order to create the database you must connect with admin user (SA and password recommended) for the very first time. For that you only need a jdbc connection.
If the database does not have a password for the SA user, you must set it with the folling command:
ALTER USER SA SET PASSWORD 'sa'
Then you can connect with a PostgreSQL client to the h2 database.