What are filters?
You can use filters while shooting to create certain moods or colours in your images. For example, you can use a black-and-white filter or a red filter to realise a special effect. A filter is a piece you mount on the end of your lens, but you can also choose to hold it loose in front. If you pick the latter, however, there's a chance your images will turn out blurry.
Why a filter system?
A filter system is ideal if you plan to work with filters. If you're not sure yet which filter you want, a filter system lets you swap filters easily. Or do you plan to work with many different types? Then a filter system is ideal for that too.
By mounting this system on your lens, you always have it nearby and can swap quickly. Don't want to use a filter? Then take it out but leave the system on. That way you can keep shooting without the system showing up in your images.
Glass or resin?
Glass filters are usually more robust and dirt-repellent than synthetic resins. The high quality is achieved here by the multi-layer coating. This is especially noticeable when cleaning, because they hardly get scratched. By comparison, synthetic resins are cheaper. When transporting resin filters you have to be particularly careful, as scratches can appear quickly. There are, however, not as many suppliers of resin filters as there are for glass.