It works by using JDBC (Java DataBase Connectivity) to connect to the database so it will have to support JDBC to conduct the test. The program generates a load by sending a series of SQL statements to the database server which is registered as a transaction. You can choose two types of interface to control - an interactive command-line interface and a GUI based interface which is called TGC (TG Controller). I recommend the latter because if you're not familiar with databases, the command line will confuse you completely.
This is certainly useful if you have issues with your database load although be warned that if you don't know basics about Oracle or MySQL databases, you could end up quite lost as it's quite technical and the instructions are sketchy.