In order to use the search filters, you first have to do a search in order to get the available fishing cabins for your desired period and location.
On top of the results, you see a blue bar with various search filters. As long as no filter has been applied, all search results are shown.
You can now select any filter you prefer in order to get the best possible selection of fishing cabins for your trip.
Note that the results will be adjusted automatically as soon as you change the search filters.