Two steps: first register the JDBC driver, then register the database. Details:
1) Click on the Services tab (it is in the top-left panel, next to the Projects ans Files tabs). Expand databases and right-click Drives, choose New Driver. In the New JDBC Driver dialog click Add and locate the JDBC driver JAR file. Once you identify the driver JAR the rest of the fields in the dialog should be filled. Click OK
2) Right-click the driver and select Connect Using. Fill out the New Database Connection dialog for your database. Click OK. A new entry for your database shows up under Database.
You can then expand the database entry to view tables and data.