DBD stands for DataBase Driver. DBI can not work without one. Each one is different, one (or more) for each Database Management System you want to connect to. If you have an installed Database like PostgreSQL or MySQL, use the DBD for that system (DBD::Pg or DBD::mysql). If you don't have a system yet, both of those are free, but require you to install both the database system and DBI and the appropriate DBD. A simpler approach if you are just getting started is to use a stand-alone driver that does not require a separate Database sytstem backend. DBD::SQLite is the most robust one currently available. The simplest to test with is DBD::DBM since it comes with DBI and doesn't require any other software to do simple tasks.