To group records, there needs to be a common value in a field so that when you sort records with this field as part of the sort order, it groups them within your layout's found set. Then Sub summary layout parts based on the same field can display group (aggregate) values such as a total, count, average... in a summary field.
Here are some examples of calculation fields you can add to this table to produce such "group by" values:
cDay: GetAsDate ( TimeStampField )
cMonth: Let ( D = GetAsDate ( TimeStampField ) ; D - Day ( D ) + 1 ) // returns date for first day of same month
cWeek: Let ( D = GetAsDate ( TimeStampField ) ; D - DayOfWeek ( D ) + 1 ) // returns date for first day of same week (Sunday)