What is the step exposure method? Under what circumstances is this mode often used?

Canon calls it exposure bracketing. It means taking multiple exposure shots of normal, negative compensation and positive compensation for the measured exposure.

Exposure bracketing has two uses:

1. When the ambient light is mixed, multiple exposures with different exposure combinations are performed to ensure that accurate exposure photos can be obtained.

2. When using a digital camera for HDR photography, you can take photos with different exposures and perform HDR synthesis later.