If you are are downloading your music, simply open i-tunes and drag and drop your music into it. Then once you plug your ipod into comp it should automatically update the ipod, if not just click the "sync" button.
Same for video, just make sure the files have been converted to compatible media files.
Or connect your ipod to itunes and once it shows up on the left hand side double click it and add the songs in the same way directly to teh ipod.
If your still struggling there are tons of videos on the likes of youtube that may explain it better. Hope this helps matey