how do i back my stuff up before i restore my ipod

See:

iOS: Transferring information from your current iPhone, iPad, or iPod touch to a new device

Note that syned media like app and music have to be in your iTunes library since synced media is not included in the iPod backup that iTunes makes.

You can transfer iTunes purchases to the computer by:

iTunes Store: Transferring purchases from your iOS device or iPod to a computer

For non-iTunes purchases you need a third-party program like one of those discussed here:

Recovering your iTunes library from your iPod or iOS device: Apple Support Communities