How can you exploit file upload vulnerabilities in PHP apps

Question

I am studying web security and want to understand how attackers exploit file upload vulnerabilities in PHP applications. My focus is on:

• Common misconfigurations in PHP file upload handling.
• How attackers bypass restrictions like MIME type checks or extension filtering.
• Real-world exploitation techniques (e.g., uploading web shells) and their prevention.
  I’m looking for insights on both the attack vector and defensive measures to secure file upload functionalities properly.