Oh, I see. So you're using some premade Python-script, but you don't know Python yourself?
I'll explain it a little bit more:
'os' is a module. Every module used in another module needs to be imported prior to using it. Insert the following line at the start of your script:
Now Python knows where it has to look for the function getcwd(), so if the next line is
movieFile = os.getcwd() + r'\planetajogos\INTRO2.wmv'
it will look into the module 'os' and search for the function 'getcwd', execute it and return the path to the current working directory, which will then be combined with the second string.
For the basics of Python have a look at various teaching sources in the web, e.g. the wiki book Python Programming. It is essential to know the basics of Python if you intend to use it.