Full screen image styling

When a user clicks on an image in a post it goes to a no-frills page with just an image on it. i would love to:
– style this page (centered, header etc). I noticed at the moment it is just body and image. no div or styling tags
– have a simple thumbnail index of other relevant images (from same post or category) – i think i will be able to work this one out.

I have tried to understand and code every major part of my website – so the fun for me is to write this out rather than use a plugin. could someone give me some hints to start.