What is the easiest way to learn prime numbers?

I'm curious, what would you say is the simplest and most effective method for someone to grasp the concept of prime numbers? Is there a particular resource or approach that you've found to be particularly helpful in teaching or learning about prime numbers? Perhaps a website, an app, or a specific technique that you've found to be particularly engaging and effective? I'm eager to learn more about the most straightforward path to understanding prime numbers.