The three support articles at the bottom of this post should be helpful.
To sync contacts with your computer, choose "Sync Contacts with" within iTunes for Windows, or "Sync Address Book Contacts" on your Mac.
You can sync your contacts with:
Notes:
- When syncing contacts, you can choose to sync all of your contacts or only selected groups. The option to sync selected items may not show up until after the first sync.
- You can select a group of contacts to which all new contacts created on your iOS device will be added.
- Additional options for syncing include syncing your contacts with Yahoo or Gmail/Google Mail. You will need to configure it with the user name and password for your Yahoo or Google account.
iOS: How to transfer or sync content to your computer - Support - Apple
iOS: Syncing with iTunes - Support - Apple
iTunes 11 for Windows: Set up syncing for iPod, iPhone, or iPad