> ## Documentation Index > Fetch the complete documentation index at: https://python4ai.codewithsiva.dev/llms.txt > Use this file to discover all available pages before exploring further. # Functions > Create reusable blocks of code ## Building with functions Functions are reusable blocks of code that do specific tasks. Instead of writing the same code multiple times, you write it once as a function and call it whenever needed. Think of functions like: * A recipe you can follow multiple times * A machine that takes input and produces output * A named shortcut for complex operations ## Why use functions? * **Don't repeat yourself**: Write code once, use it many times * **Stay organized**: Break complex programs into smaller pieces * **Fix bugs easier**: Change code in one place, affects everywhere * **Test your code**: Test each function separately ## What you'll learn Create your own functions Pass data to functions Get results from functions ## Real-world examples Functions are everywhere in programming: * `print()` - displays text (built-in function) * `len()` - counts items (built-in function) * `calculate_tax()` - your custom function * `send_email()` - your custom function ## Let's begin! Start by learning how to create your first function. Create your first function