In the beginners tutorial it tell you to creat a new directory to save your programs in.I did that and then i saved the program as mileage.py.Then when i went to DOS to open it will only let me get to the new folder and when I type in mileage.py it says:

'mileage.py' is not recognized as an internal or external command,batch file or operable program

What am I doing wrongll!!!