To access your customer report head to Reports > Top 100 customers.
This will display a list of your top 100 customers within the date range you selected. You can change the date range by selecting a date from the drop down calendar that appears.
The report will show:
Customer name - you can select on the customer name and it will take you directly to the client profile
Orders - amount of orders the customer has had
Total order value - an overall total of their orders
Average order value - how much their average order costs
Your top customer is based on the amount of money they have spent not the amount of orders they have made.
You can also 'Export' this report to view it in a spreadsheet, where you can then save/ print if needed.