Hi mark142857,
Welcome to the Support Communities!
Now that you have your Apple ID created, the links below will provide information on how to enter or update your billing information. I've also included some general information on the iTunes Store for you.
Using an existing Apple ID with the iTunes Store, Mac App Store, and iBooks Store
http://support.apple.com/kb/HT2589
Apple – iTunes – Everything you need to be entertained.
https://www.apple.com/itunes/
iTunes: Turning on iTunes menus in Windows 8 and 7
http://support.apple.com/kb/HT5610
Once iTunes is installed, click on the Store command on the menu bar, and sign in to your account using your Apple ID and password.
iTunes Store: Authorize or deauthorize your Mac or PC
site:apple.com authorize computer itunes
Do you have a copy of your Music folder from your old computer? You can add your music to your new iTunes library:
Adding music and other content to iTunes
http://support.apple.com/kb/HT1473
Cheers,
- Judy