where do blog catagories link to?

so ive styled my blog page which is the index.php page but when i click on categories or on the title im sent to another page which will need styling, which page does wordpress use for those links?

i assumed categories would be category.php and the other would be page.php but when i open it it seems to still have a <section> tag showing even when there is no section tag in the page.php

the links will normally go to something like ?/p=427 and ?/cat=321

thanks