Open your browser and go to YouTube or any site with Flash Videos.
Next pick your favorite video and wait until it's fully loaded.
Next go to your /tmp folder and your video should be labeled Flash with some random letters and numbers.
Copy this file to another folder.
Ex. Your Desktop Folder.
That is it! You just saved your Favorite Flash Video.
Please do not copy copyright material. It is illegal and you can get fined or sued. It's just not worth it.