When you open a list, the Filter view lets you refine it according to how its criteria are distributed.
My list contains 609 companies. When I open it, the Filter view lets me refine it according to its breakdown by criteria. I select the filter or filters I want: for example, I only want companies with turnover between 2 and 50 million in the manufacturing industry.
I apply my filters with the Apply button and immediately see the number of companies left. I can switch these filters off at any time with the Reset filters icon.
I can also create a new list from the 164 companies I obtain: once I have selected them, I click New list. I could have applied these filters to contact or website lists just as well: in a contact list, for instance, I can filter directly on contacts whose email is validated.