Docker has revolutionized application deployment. This guide will help you get started with containerization.

What is Docker?
Docker is a platform for developing, shipping, and running applications in containers. Containers package your application with all its dependencies, ensuring it runs consistently across different environments.

Key Concepts
1. Images: Read-only templates for creating containers
2. Containers: Running instances of images
3. Dockerfile: Instructions for building images
4. Docker Compose: Tool for defining multi-container applications

Getting Started
Install Docker and create your first Dockerfile:
```
FROM php:8.2-fpm
WORKDIR /var/www
COPY . .
RUN composer install
```

Best Practices
- Keep images small
- Use official base images
- Minimize layers
- Don't run as root
- Use .dockerignore

Docker Compose
Manage multi-container applications easily:
```
version: '3.8'
services:
app:
build: .
database:
image: mysql:8.0
```

Docker simplifies deployment and ensures consistency across development, testing, and production environments.