To build a blog application with PHP, you will need to follow several steps:

1. Set up your development environment:
– Install a local server like XAMPP or WAMP that includes Apache, PHP, and MySQL.
– Create a project folder for your blog application.

2. Create a database:
– Create a MySQL database to store blog posts and other blog-related data.
– Define tables for the blog posts, authors, categories, and any other required entities.

3. Create the user interface:
– Design a user interface for your blog application using HTML, CSS, and JavaScript.
– Create templates for the blog posts, categories, author profiles, etc.

4. Implement the PHP backend:
– Create a PHP script to handle requests and responses for various actions such as creating, reading, updating, and deleting blog posts.
– Use PHP functions and libraries to interact with the MySQL database.

5. Implement user authentication:
– Create a user registration and login system to allow users to create and manage their own blog posts.
– Use PHP sessions or tokens to manage user authentication and authorization.

6. Integrate the user interface with the PHP backend:
– Connect the frontend templates with the PHP scripts to display blog posts, categories, authors, etc.
– Implement forms and submit actions for creating and updating blog posts.

7. Implement additional features:
– Add features like commenting on blog posts, searching for posts, categorizing posts, etc.
– Use PHP functions and libraries to implement these features.

8. Test and debug:
– Test your blog application by creating and managing blog posts, logging in and out, and performing various actions.
– Debug any issues or errors that arise during testing.

9. Deploy the application:
– Upload the blog application to a web server to make it accessible to others.
– Configure the server environment to correctly run your PHP application.

10. Maintain and improve the application:
– Monitor the application for bugs or performance issues and fix them as needed.
– Continuously improve the application by adding new features, enhancing the user interface, etc.

Remember to follow best practices for security, such as validating user input, sanitizing database queries, and protecting against SQL injection and cross-site scripting (XSS) attacks.