Before we get coding, let's make a list of the things that the video sharing application should do:
Be able to show a home page with a main video and a list of all the other items that have been recently uploaded
Be able to register a user so that they can upload a video
Allow users to log in and log out of the application
Only allow registered users to upload a video
Convert a video into a format that is web viewable
Create a large poster image of the video
Create a thumbnail version of the poster image
Allow registered users to comment on a video
Display comments underneath a video
That seems to be enough to get on, so let's start implementing these features.