What will happen if I choose one filter and then apply another filter over the first one?

Choosing one filter will narrow down your options. Choosing a second filter over it will narrow down your options further. For example:  If you choose filter of Active listings, then out of your all products (Active and inactive), only the ones Active will show. Then, if you apply a second filter of 5 or more over this Active filter then you will be able to see only those active products which have stock count of 5 or more.