When I open I-tunes on windows 8 the library doesn't automatically download.
When you say "download," you are referring to your iTunes library syncing to the iPod, correct? Not something downloading from the Interent to your computer...
If you want to use automatic syncing, you need to set it up in iTunes. First, if the iTunes sidebar (along left side of window) is hidden, from the menu bar, under View, select Show Sidebar. The iPod appears under DEVICES in the sidebar, when connected.
Select the iPod in the sidebar. The iPod's Summary screen appears to the right. Toward the top, there is a bar of buttons, starting with Summary; click on Music next toSummary. This Music screen is where you tell iTunes how to sync songs to your iPod.
Check the box for Sync Music. This setting enables automatic syncing. If your iTunes music library is small enough to fit on the iPod's storage, you can choose the option to sync Entire music library. That syncs everything that is music. Otherwise, choose the option to sync Selected playlists, artists, albums, and genres. Then, select (checkmark) what you want on the iPod from the lists below. One convenient way to set this up is to create one or more playlists in your iTunes library, and put ALL of the songs you want on the iPod on those playlists. (Or you can use existing playlists.) Back on the iPod's Music screen, select the playlists under Playlists.
When you click Apply, the songs in your selection(s) sync to the iPod. Going forward, to update songs on the iPod, update those playlists in your iTunes library (add/remove songs). The iPod does not need to be connected. The next time you connect the iPod (or click Sync if already connected), iTunes updates the iPod with the same changes automatically.