Create a Filter like Online Shopping websites in ASP.Net

Well if you see the REFINE Section , that's just a little trick :

Create a gridview with only one template column ,set autogeneratecolumns = false , then in that template column put one checkbox and two lables , one for displaying the sizes and one for displaying the count of those sizes by group (Implement SQL Grouping Query here , you have to create a view for that) , then in checkbox oncheckchanged event redirect the page and pass the category size in url to another page , and in other page load event read that URL and show the products related to it .....

May be you can checkout the following they can act as a base for you to start

1. How to filter data using multiple CheckBoxes from CheckBoxList in GridView in ASP.Net
2. Filter DataList records based on multiple CheckBoxList selections in ASP.Net
3. Filter Gridview using checkboxlist control or multi select dropdown list control
4. Filter ASP.Net GridView data based on CheckBoxList Checked Items