Purpose of using clapboard on set is to sync the audio with picture easily during editing. It is a life saver method to get the post –production process done.
As for audio information, it is the camera assistant who call outs the shot and take numbers. It is wise to get in the habit of using proper on-set commands. The assistant director, who should be running the set, handles this routine:
Assistant director: “Quiet on the set/on location” (this notifies everyone that you are ready to film).
Assistant director: “Roll sound.”
Sound recordist (once audio is being recorded): “Rolling” or “speed.”
Camera assistant: “Scene _____ take _____.”
Assistant director: “Roll camera.”
Camera operator (once camera is recording): “Rolling” or “speed.”
Camera assistant: “Marker” (then claps using the slate).
Camera operator (when ready to begin filming the action): “Camera set.”