You don't need to visit Youtube, you can use the search engine built in the interface. Find the videos you want to download, because that search box gives you access to Youtube video catalog.
Select the elements you want to download and press the button 'download' when you'll have selected all the videos you want to download.
The menu of Tooble gives you access to different categories of Youtube (popular, recent, favorites, top valued, top commented...)
Finally, when the videos are downloaded, they will be ready to play on your iPod. Don't worry about formats Tooble has done it for you.