podcast Tab on Categories

Hi All,

I try to play with podcast , and i notice that in iTune apps on win XP , i notice there are 3 TAB.

Podcasts
Categories
Unwatched

May i know what is the purpose of Categories TAB ?

May i know why the cateogories TAB have only 1 icon , but there are many file inside , as when my cusor touch the icon , i can see there are many image appear.

Hope some one can share with me.

Paul