I want to add a drop down box in my page, so that the user will select the items' ordering.
e.g he will choose ordering by name, width, color (width & color will be extra fields which I will add) and th items will be ordered by the user 's choice.

Here for example, you can choose Sort By: Best Selling, Product, New etc.

How can I do this with k2?

Hello,

You will need a 3rd party extension (can't remember a name) in order to add extra field ordering.

The select box can be populated with menu links which have different ordering settings.