Linking code

Hello,

This is kind of hard to explain, but I made a website with some pictures. I have a main page with links to the picture pages, there are something like 8 pages with pictures.
When I change something at one page I need to manualy change it at the other pages. Is there some way to have one main file with all the code. And that the other file with the pictures are linked at some way to the main file. So I don't need to change every page manualy. I tried to do it the same way as the style.css works. But I can't get it to work.