How to create headphone mix for zed r16

Hi,
I'm 17 and currently studying a levels, music tech part of one.

I'm working in a studio which has been set up by a professional engineer, everything hooked up.

We are running Logic Pro 9 through a zed r16 to a set off logic speakers.

So my problem is;
There is one thing that wasn't seen to, and am now facing problems with.

I've come to record vocals for songs, and I have no idea how to have the song play into the headphones in the booth.
I am aware I have to make a headphone mix, but dear god I have no idea.
I've been using logic for about three years now, so am still a noob.

Help would be greatly appreciated. Thank you!

Jordan