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Simply put, ev is exposure. For example, it's dark now, which can improve the exposure. If it is too bright now, you can reduce the exposure. You aim at an object, choose different values, and you will know at a glance.

ISO refers to the sensitivity of CCD. If the light is bad or the object is moving, you need high sensitivity, otherwise, you need low sensitivity.

Note, however, that the higher the ISO, the more obvious the noise will be. Image quality. (This is the same. You set different sensitivities and then you can see the maximum magnification of the picture at a glance. High sensitivity, bright photos, but many mottled spots)

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