Reports - Aggregating
Aggregating columns to collapse repeated rows in a report is an advanced feature.
You will typically not need this, but if you do, there is a video.
You can, and often need to, aggregate hidden Database ID columns in a report. Always use a "Min" or "Max" aggregate on these columns (it doesn't make a difference which you choose). Using "Count", etc., will cause the report to add another instance of the Database ID column the next time the report is edited.