1. Plug your iPod into your computer.
2. Bring up iTunes
3. Make sure your connected to the internet, but you don't need to bring the internet up. Also make sure you have an iTunes account and money on an iTunes gift card or a credit card to pay with.
4. Click on iTunes store.
5. Use the buttons at the top and the search bar to find the video you want.
6. Click the buy button next to it.
Detailed enough for ya?