1. Click on Administration > System > Edit Reports
2. Choose the option to create a new report
3. Choose to add a new 'Custom Section' to the report
4. For this new custom section, choose the appropriate reportable entity (e.g. Incidents corresponds to the TST_INCIDENT table, plus all its joined entities in an easy to report-on view)
5. This will generate a SQL query that looks like select value R from SpiraTestEntities.R_Incident where PROJECT_ID = ${ProjectId}
6. Then click on 'Generate Default Template'
7. This will populate the XSLT for generating a simple table containing the data in this query
8. Save the report

You can then use more advanced SQL to join tables, do aggregations, etc.