Functions are fundamental building blocks in programming that allow you to organize and manage your code efficiently. A function is essentially a self-contained piece of code designed to perform a specific task. To define a function, you start by giving it a name and outlining the actions it should carry out. This definition includes specifying any inputs the function might need, known as parameters, and the actions or operations to be performed using these inputs.

Once a function is defined, you can call it from other parts of your program. Calling a function means executing the code within it. When you call a function, you provide the necessary inputs, and the function processes them to produce an output or carry out its intended task. This allows you to reuse the same function multiple times without rewriting the code, making your programs more modular and easier to maintain. Functions also help in making your code more readable and organized by breaking down complex problems into smaller, manageable parts.