Yes, you can sync multiple devices to one iTunes library. Just connect it and sync.
If you wish to have them sync with different subsets of the library, e.g. using the "sync selsected playlists" option, you can set them when the device is connected, and iTunes will remember each device independently for the next time it is synced.
hello, where is the 'sync selected playlist' option?:)
Connect your iPod to the computer and give it a minute to register. Look for the iPod's name in the left pane of iTunes, and click it. In the new row of Summary, Music, Movies, etc, click on Music, and then on "Selected playlists..."