How to backup my contacts to my PC?

You should have been syncing your contatcs with your computer from day one.

iPhone User Guide (For iOS 6.1 Software)

Open itunes, connect iphone, select to sync contacts, sync.

Make sure that you have at least one unique contact on your computer before dooing so, giving you the option ot merge the data.

• To start, install iTunes on your computer if you haven't already (http://www.apple.com/itunes)
• Every time you back up your iPhone to iTunes on your computer the contacts are backed up.
• Every time you back up your iPhone to iCloud your contacts are backed up.
• You can sync your contacts with an address book app on your computer: Connect the iPhone to your computer, click on its name in iTunes, click on the Info tab at the top, scroll down and check "Sync contacts" and choose an app to sync to. Make sure there is at least one entry in that app on your computer, then click the Sync button.
• If you have an email account hosted on an MS Exchange server contact sync will be automatic and real time.
• You can set up an iCloud account with your Apple ID and sync your contacts to iCloud. If you have a Mac this will also sync them to your computer; if not you can managed them in iCloud by going to https://www.icloud.com and logging in with your Apple ID.
• You can also sync with your Google address book