what is the concept behind None?

Functions in Python always return something. If you don't explicitely specify a return value with return ..., your function will return, by default, None.

If you don't enter a valid input, the return statement of your function won't be executed, so order() returns None, which gets printed as the string 'None' after that.

You could test the return value:

choice = order()
if choice is not None:
    print(choice, " will be ordered soon!!")

so that this won't print in case you didn't make a valid choice.

But you probably would like the user to try again until he submits a valid choice:

def order():
    while True:
        try:
            count = int(input("How many order ? "))
            return count
        except Exception as e:
            print("Kindly enter in numbers")
            print("Example :- 1, 2, 3, 4, 5 etc..")

choice = order()
print(choice, " will be ordered soon!!")

Sample output:

How many order ? e
Kindly enter in numbers
Example :- 1, 2, 3, 4, 5 etc..
How many order ? r
Kindly enter in numbers
Example :- 1, 2, 3, 4, 5 etc..
How many order ? 4
4  will be ordered soon!!

On exception, call into the same function to retry:

def order():
    try:
        count = int(input("How many order ? "))
        return count
    except Exception as e:
        print("Kindly enter in numbers")
        print("Example :- 1, 2, 3, 4, 5 etc..")
        return order()
    finally:
        print("Thanks to choose our service.")

In case of an error (if string is provided as an input for example), your code will go to the except block which has no return value (None is the default return value) and that's why your choice variable will be None.

If the input can't be converted into an integer, the exception will be triggered and have no return value since it only display some messages. YOu can return 0 if the value is not a valid number.