When an actor "slates" for the camera they simple state their full name, and sometimes their height and/or age (if they are under 18). For example, if the actor's name is "Michael Rubinger", to slate the actor would say "Michael Rubinger".
A headshot is a photograph of an actor's head and face. It is designed to provide Casting Directors with an accurate visual representation of what an actor looks like at this current point in time.