Slating means to state your name and the part you are reading for. So, once the casting director tells you where to stand in front of the camera, stand in that spot. This will usually be marked on the floor with an "X."
The casting director will usually tell you what to slate. For example, "slate your name," or "slate your name and the role you are playing." This simply means look into the camera and state your name and the role you are playing. If the casting director asks for additional information, state that as well. Speak clearly and enunciate. If you have to state your telephone number, say each number and don't rush through it.
The casting director usually asks for "profiles" after you slate. For this, all you need to do is turn to the left side and then to the other. This allows the to see how your profile looks on camera. They may pan the camera up and down for full body shots. If they do, stay still.