How to turn on AF51 on a Nikon D800?

My father was wondering how to turn on the AF51 (51points or something) on the Nikon D800. I have no clue of what he is talking about because I don't know anything about cameras lol. So I was hoping that someone can help me out here with it.

I have no clue what he's talking about either - AF51? What is that? There's AF, as in Auto Focus.
There's a switch on the lens.

Jim - he means to select the 51 points for the Autofocus.

Your father should have a camera manual when he bought the D800 - get him to read it! (it's a bloke thing, I know, not reading instructions)