Functions in PHP are like little tools that you can create and reuse throughout your code. Let's say you have a task that you need to perform multiple times, like calculating the area of a circle. Instead of writing the same code over and over again, you can create a function to do it for you. When you define a function, you give it a name and specify what it should do. Then, whenever you want to use it, you just call the function by name and it will execute the code within it. You can also pass arguments to a function, which are like inputs that the function can use to perform its task.