Here's an easy example of a Docker Compose file for an app with PHP and MySQL. In this case, we use PHP as the web server and MySQL as the database.

1. Create a directory structure for your project:

/myphpapp
|-- app
|   `-- index.php
|-- docker-compose.yml
`-- Dockerfile

1. Create the PHP application file (app/index.php):

<?php
$host = 'mysql';
$user = 'root';
$pass = 'password';
$db = 'mydatabase';

$conn = new mysqli($host, $user, $pass, $db);

if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

echo "Connected to MySQL successfully!";
?>

1. Create the Dockerfile (Dockerfile):

FROM php:7.4-apache
COPY app/ /var/www/html

1. Create the Docker Compose file (docker-compose.yml):

version: '3'
services:
  web:
    build: .
    ports:
      - "8080:80"
    depends_on:
      - mysql
  mysql:
    image: mysql:5.7
    environment:
      MYSQL_ROOT_PASSWORD: password
      MYSQL_DATABASE: mydatabase
      MYSQL_USER: user
      MYSQL_PASSWORD: password
    ports:
      - "3306:3306"

Explanation:

• The web service uses the official PHP 7.4 Apache image, builds the Dockerfile in the current directory, and maps port 8080 on the host to port 80 on the container.

• The mysql service uses the official MySQL 5.7 image. It sets environment variables for the root password, database name, and user credentials.

• The depends_on attribute ensures that the web service starts only after the mysql service has started.

1. Run the application:

Navigate to the directory containing your docker-compose.yml file and run the following commands:

# Build and start the services
docker-compose up

# Access the PHP application at http://localhost:8080

This is a simple example to help you begin. In a real-world setting, you would probably want to protect your MySQL login details and think about more settings for both PHP and MySQL services, depending on your needs.