You haven't read my above reply properly - you can only view the 'manage devices' section on a computer's iTunes via the Store > View Account menu option, and that won't let you add a device to your account anyway, you can only use it to view and/or remove devices from it.
Do you have 'automatic downloads' turned 'on' on your iPod ? If you want purchases that you do on your iPad to also download on your iPod then you need to have Settings > iTunes & App Store > Music turned 'on' on your iPod. After you turn it 'on' on your iPod then any future purchases that you do on your iPad should also download on your iPod - for purchases that you've already done then you may be able to download them via the Purchased tab in the iTunes store app on your iPod.