The postgresql-server package includes the programs needed to create
and run a PostgreSQL server, which will in turn allow you to create
and maintain PostgreSQL databases. PostgreSQL is an advanced
Object-Relational database management system (DBMS) that supports
almost all SQL constructs (including transactions, subselects and
user-defined types and functions). You should install
postgresql-server if you want to create and maintain your own
PostgreSQL databases and/or your own PostgreSQL server. You also need
to install the postgresql package.