Final answer:
Partially pushing the two-part exposure button on a camera activates the autofocus and light metering, preparing the camera for a properly exposed photograph.
Step-by-step explanation:
If a camera or another device with a two-part exposure button is being discussed, pushing the switch typically refers to initiating the process of focusing and metering the exposure on the device before taking a photograph. On most cameras, partially depressing the shutter button activates the light meter and autofocus, and fully depressing the button captures the image. This two-step approach allows photographers to ensure the focus and exposure are set correctly before taking the picture.