Note that using loops you can call any function multiple times, even your own functions. Let's suppose we defined this function:

def celsius_to_kelvin(cels):
    return cels + 273.15

That is a function that gets a number as input, adds 273.15 to it and returns the result. A for loop allows us to execute that function over a list of numbers:

monday_temperatures = [9.1, 8.8, -270.15]

for temperature in monday_temperatures:
    print(celsius_to_kelvin(temperature))

The output of that would be:

282.25
281.95
3.0

So, in the first iteration celsius_to_kelvin(9.1) was executed, in the second celsius_to_kelvin(8.8) and in the third celsius_to_kelvin(-270.15).

That's just something to keep in mind.