The reg-app has been used and tested with PostgreSQL (> version 9) until now. It should also work with any other JPA compliant database, which Hibernate can use.
Installation of Postgres is out of scope of this document and dependant on the operating system you are using.
Please create an empty database for the product you will use. For PostgreSQL this can be achieved by:
su postgres createuser -P regapp-user createdb -O regapp-user regapp exit
Edit your pg_hba.conf file to allow authentication via md5 for regapp-user from your host, which is running the application.
Next step: Install/Configure Application server