Filters are a great way to get artistic with your photographs. They can add all types of functionality like a change in color or in the depth of the photo, etc. Most gel type filters and square glass filters are held on by special filter holders. For some holders you will need an adaptor ring so it can fit to your specific lens filter size. Some filter holders are threaded at the front enabling them to accept additional filters, lens hoods or to combine multiple filter holders for special photographic effects. They can also rotate and move the positioning of graduated filters.
Make sure your filter holder doesn't interfere with the rotation of your lens front or the camera's auto focus function. Filter holders come in various sizes, materials and colors and can range in price from about to $20 to $150. Always ensure the lens filter will attach to your brand of lens and camera.