Open iTunes > Help > iTunes Help
Under Contents > Expand The iTunes Store > Select Managing Your iTunes Store Account.
You will see the following topics which should answer your questions.
* Managing your iTunes Store account
* Setting up an iTunes Store account
* Signing in or out of the iTunes Store
* Changing your iTunes Store account information
* Authorizing a computer to play iTunes Store purchases
* Viewing your purchase history
* Making sure you have all your iTunes Store purchases
* Moving your iTunes Store purchases to another computer
* Using iTunes behind an Internet firewall
If you want to copy the contents of the ipod to the PC you will need to buy a 3rd party program. Use Google to find one on the internet.