What is a JDBC driver? It is a driver for accessing a database in Java. How to get one? Just google name of your database and JDBC. For example to get JDBC driver for MySQL database google "mysql jdbc". For Oracle "oracle jdbc". For postgresql "postgresql jdbc".
Be sure to download correct JDBC driver for your database. For MySQL database you should usually download latest version. It is also best practice to always consult documentation. Oracle and postgresql has different JDBC driver for each version.