what is the use of function in python code example

Example 1: explain def in python

def greet(name):
    """
    This function greets to
    the person passed in as
    a parameter
    """
    print("Hello, " + name + ". Good morning!")

Example 2: function used in python

def hello():
  name = str(input("Enter your name: "))
  if name:
    print ("Hello " + str(name))
  else:
    print("Hello World") 
  return 
  
hello()