Go to https://dofsimulator.net/en/
which is actually a depth of field simulator, but it works well for showing field of view.
When that screen opens you will see a caricature of a woman, hands on hips and the bottom of the image is roughly mid-thigh and the top slightly more than her full head. Peruse down the left edge and you will see the image is from a 35mm format, an 85mm lens at f/1.4 and the subject distance is at 3 meters (just short of 10 feet). In the "Sensor size" field, use the drop down menu to show APS-C (Canon) and note the image change. You now see the caricature showing from approximately the waist to about the top of her head. Check and you will note the lens is still shown as 85mm at f/1.4 and the subject distance is still 3 meters. The change in what you see is totally due to the change in sensor size. An analogy would be you have two cameras around your neck, one full frame and one APS-C, both with the same focal length length lens. The two images are what you would see with the two cameras.
Play with the simulator to see the changes and once you understand focal length and sensor size change the scenario for the intended purpose of the simulator, depth of field. Go back to the original screen settings, 35mm format, 85mm focal length and f/1.4 aperture. Note the background of the image is quite blurry. Change the aperture to f/16 and you now see that the caricature is in front of a landscape that includes some buildings.
You can use the sliders to make changes as well.
