Hi Giovanni,
Here are the steps:
1. BI Services menu => Query Wizard => Build SQL Query.
2. Verify that the correct BI_JDBC system is selected (in case there is more then one).
3. Write the query according to available tables.
4. Verify / OK.
5. A Data Service is created in the model for the query. Connect whatever model elements you need to it.
Thanks,
Udi