Filter tools usually exist on collection page(s) as they allow you to set parameters so you only look at certain items at once, or so that it sorts the items in a specific order.
Most commonly you'll see fashion filters for the type of clothing (shirts, pants, dresses, skirts, accessories, etc.) or to sort the items by (newest, most popular, best selling, A-Z, Z-A and either highest price to lowest price or lowest to highest).