Using the WordPress Admin Panel with a custom site

So I’m learning how to build my own portfolio website with php. I’ve got most of it done, the last thing to add in is the blog section. I wanted a simple way to create, manage, and display posts, so I figured I would use WordPress. I installed it in a ‘/blog’ folder on my site and began designing my blog page. That’s when I noticed the header to log in wasn’t there, and the admin panel no longer worked, displaying things like “/blog/edit.php was not found on this server.” It displays posts on my site just fine, but how do I use WordPress to create and manage posts on a custom website?