I’ve been making a few customisations to my theme using the child theme.
I wanted to change the layout for all of my pages, category pages & posts pages (but NOT my home page) so that the navigation bar is below the page heading (e.g Travel above nav bar)

Also, is there a way for me to show the category as a title on my actual posts?
For example the title as shown on /category/travel/ but shown on the post /travel/welcome-to-travel/ above the featured image?

I understand this is probably to be done through php however I have absolutely no understanding of it and which files to use and where abouts to put the code into.
If there a way to do this through css that would be great but otherwise idk what to do.

IF anyone could help that would be awesome – thanks

I can’t tell you which files, however, or which changes to make, because it looks like you are using a commercial theme. You’ll need to ask your theme’s developer for help with this.