Do you have your results page setup to search based on an item or category id? This will be the first step, you must have the results page configured with the DataAssist Search server behavior and have it setup so that you are searching the id column or category column from your products table.
Once you have it setup like this you can use the links to pass in the search values that this page will look for.
I would suggest that you get this setup with the DataAssist wizard to have it create the search and results pages for you, but do not specify any of the search criteria in the wizard. Once the pages have been created edit the DataAssist Search server behavior on the results page to look at the column you would like to search.
Once you have the results page working correctly with a search page you can then go and add in parameters to the links in the menu to have it display the results for that item or category.
If you have any trouble with this you should take a look at the getting started guide and other resources that are available on the DataAssist support page:
If you have any further questions about any part of this please let us know and we will help you with whatever we can.