This report shows you the 25 top selling products based on sales revenue for the specified date range (by default this report will show today's date range)
Keep in mind that by default that this report will by default also only show you the sales for the outlet that your currently logged into the POS with, however you can select more outlets to view by clicking on the drop down menu in the top right hand corner here:
You also have the ability to choose whether to show the Sales by Sales $ Amount or by Sales Qty Sold amount by selecting the "Show by Volume" check box
You can then choose to display the results by Style for example you have T-Shirt that comes in Red , Blue , Black and White in Sizes 6, 8 , 10 , 12 , 14 and those are part of the 1 product style, now you don't want to see which size or colour sells best but rather see how that style is performing against other styles then you would check this box.
This report would quite often be used to see what is selling best for a given period at a glance and allow you to prepare for the future.