Single posts not displaying as I would like

Hello,

I think I may have done this all wrong! I’m getting very confused!

My site is at https://www.marble-design.co.uk

I wanted the blog in the homepage so I made my index a php file and put in the necessary php code in the blog content bit etc.

When I go on a single post I am not sure it is using the single.php files, I have been trying to get the single php file to get a different header, so that the single post will show on a page without the slidedeck at top of page. I have also tried changing the index.php in theme file to grab a different header and the page.php too.

Are there any other files that might be being used when i select a post?

any advice appreciated
thank you in advance