When you plug in your iPod Touch you will likely have the "Welcome to Your New iPod" screen come up. This will give you a couple prerogatives, which are to register your iPod Touch and to set up a brand new account with iTunes. At the bottom will be two buttons: one that says Register Later and one that says Continue. If you want to begin registering your iPod Touch you can just hit Continue. The next screen will be one for you to sign into an iTunes account using an Apple ID.
If you already have an Apple ID you can just enter it here to register your iPod Touch. You will likely already have an Apple ID if you have had a previous iPod or an iPhone. If you enter your Apple ID then you will be taken to a screen with all of your previously entered information. If you are getting a brand new Apple ID for your iPod Touch then you will enter information, such as contact information, location, and optional things about your character and iPod preferences.
You may also want to take the time to turn off the promotional emails, unless you do not mind receiving these in your email inbox. Just hit the submit button at the bottom when you are done with the registration information screen and you will be finished. From here, you will just be taken to the normal iPhone display screen. This lists all of your iPod's technical information, then have tabs for different types of content you can put in there.