WP is different than PHP code. Content is stored in a database, and displayed via template files, which come with your theme.
Which template displays your content? Take a look at the Template Hierarchy (ask the googles/bings/ducks, or look in the Codex via the link below). For instance, a page is usually displayed with a template file called ‘page.php’ in your theme folder. If you want to add code to a page, then copy that template file, give it a new name, then add your code in the proper spots.
Too much info to try to explain here. Perhaps build your understanding of WP by starting here: https://codex.wordpress.org/Main_Page . There are also tons of sites that can help with your knowledge; one is WPBeginner . You can find more via the googles/bings/ducks.