The add-on has single configuration, datasource. Datasource contains information to connect to a specific database and you can define multiple datasources. Some custom fields of the add-on needs to connect to database and defining all database connection information in centralized location will simply adding new custom fields. You don't need to define datasource for each field separately, a single datasource can be shared between multiple fields.
Clicking on 'Datasource' link under 'Custom Fields++' section of add-on administration page displays list of existing datasources.
Adding or modifying an existing datasource is very similar; You need to specify datasource name, database's JDBC URL and username/password for connecting to database. When you click the save button connection information will be verified. If there are any problem connecting to database you won't be able to save it.