{Magazine Basic} Help! Where do I put in my ad code?

Hi,

I am stuck. I want to put an adsense ad on my homepage, under a post.

Club Penguin School And Skate Party 2014

But I have no idea where to insert the code. What theme file do I need to put the code in, and where?

My site is https://clubpenguinspace.com if you need to look futher.

Thanks! ??