To share your iPhone’s Internet connection with your desktop or laptop via a USB cable you must have iTunes installed on your computer.
Providing this has been completed Internet sharing vis USB cable is a very simple task

iOS 4.3 and later

You can check iOS version in Settings > General > About > Version

• Connect iPhone to the PC via USB cable
• On iPhone: Settings > Personal Hotspot > ON

iOS older than 4.3

• Connect iPhone to the PC via USB cable
• On iPhone: Settings > General > Network > Internet Tethering > ON