Here’s how to use a magnetic ND gradient filter: 

1. Attach the magnetic holder: The filter typically comes with a metal ring that attaches to your lens. The ring is magnetic, so it sticks to the holder securely.
2. Position the filter: The ND gradient filter usually has a dark portion that starts from the top or bottom of the frame and fades to clear. Position the darker part of the filter over the area you want to reduce light exposure, such as the sky in a landscape shot.
3. Adjust the gradient: Some magnetic ND gradient filters allow for adjusting the position of the gradient transition. You can slide it up or down to better match the scene you're shooting.
4. Check exposure: After setting up the filter, adjust your camera settings (aperture, shutter speed, ISO) to get the proper exposure. The ND filter will help prevent overexposure in bright areas, especially when shooting with a slow shutter speed or wide aperture.
5. Take your shot: With the filter in place, your camera should now capture the scene with more balanced exposure, preventing the bright sky from being overexposed while maintaining detail in the darker foreground.

In summary, this filter is perfect for controlling the exposure in situations where there’s a significant difference in brightness between the sky and the ground, like when photographing sunsets or landscapes with a bright sky and darker ground.