There are a huge number of filters that you can use when taking photos. They all have their advantages and disadvantages. For example, there are filters for a smartphone, filter sets for cameras and separate screw-on filters that you can use per lens. As a professional photographer, I use a filter set that allows me to direct the viewer to the point I want. For example, think of a sunset at the water, a nice boat in front of it, some pebbles and the composition is beautiful... But if you want to take the photo, either the sky is well-lit or the foreground is well-lit. With such a filter system, you can bring that back into balance by placing a dark piece of glass in front of the dark sky, also called a gray gradient filter . This allows you to capture everything in 1 photo.
If you want to get a bit more creative, you can also use an ND filter. This filter allows you to use a long shutter speed, which is often used to make water completely smooth or to make people disappear on a busy square. This filter is also available for smartphones ! There are many more filters and possibilities, but if you want to get started with it, I can definitely recommend that you delve into it further.