How to filter data with user inputs

I need to do something, I think pretty easy…but I can’t figure out how to do it.

I’m building a custom module, from a custom db table. The data comes from a flash site, so I can’t use a “page view” strategy.

I need to show how many contents in a certain category has been visited…
Is there a way to have something like a select input where the user choose the category?

I’m able to put the parameter at the end of the url, and display the data filtered…but how I can make the user choose the category?