What exactly is it that you want to know.
A podcast is a snippet of audio/video program that you typically download to your itune first, then to your ipod. I say typically, since there are other sites where a podcast can be downloaded and apps that would let you download podcast directly in your iphone or other cell phone (no ipod needed).
Now, to download it, goto itunes store and click on podcast. Go over variuos podcasts and select the one you want. Once the podcasts are downloaded to you itune, connect your ipod and it should automatically download (sync) into your ipod. Next, goto your ipod's MUSIC (or VIDEO if it is video podcast)> Podcast (I hope I am not forgetting all the submenus) and select the podcast you wanna listen to.
There are podcasts for every subject, from business, work, science to music, movies, sports etc.