Please provide data as tables built in post (Advanced editor) or attach file. Also, post code as text between CODE tags. Images are not appreciated as cannot copy/paste.
You want an aggregate query. Access has a wizard for that. In query design view click Sigma (Totals) icon on ribbon.
Need to deal with time portion of value. Consider something like:
Code:
SELECT ClientNumber, Count(*) As CntVisits FROM ClientVisits WHERE DateValue(DateOfVisit) BETWEEN [enter start date] AND [enter end date] GROUP BY ClientNumber ORDER BY ClientNumber;
Instead of aggregate query, could build a report and use its Sorting & Grouping features with aggregate calcs. This allows display of detail data as well as summary info.