You've used print() and len() since lesson 1 — those are functions someone else already wrote. Today you write your own.
def greet(name): defines a new function called greet that takes one input — name — called a parameter. Everything indented underneath is what it does each time it's called. greet("Rodas") is a call — "run that recipe, using \"Rodas\" for name."
Notice you wrote the logic once but used it twice. That's the entire point of a function: write it once, call it as many times as you want.
Functions can hand a value back with return:
return is different from print — print just displays something and the value disappears. return hands the value back so you can store it in a variable and use it later, like result above.
Functions can take more than one parameter, and can have defaults:
exponent=2 means "if nobody says otherwise, use 2." power(3) uses the default; power(3, 3) overrides it.
Your turn
Write a function is_even(number) that returns True if a number is even, False otherwise. Test it on a few numbers.
You now have everything you need for your first real project. Next lesson: a quiz game, built from scratch.