Ever been stuck in a situation where you need to get a device online but there's no nearby Wi-Fi? As long as you've got an iPhone with a 3G or 4G data connection with you, your problem can be easily solved using Personal Hotspot.
Personal Hotspot is a feature of iOS that lets iPhones running iOS 4.3 and higher share their wireless data connection with other nearby devices via Wi-Fi, Bluetooth, or USB. In this scenario, the iPhone acts like a wireless router for the other devices, transmitting and receiving data for them. An iPhone 4 or newer is required for Wi-Fi connections, though an iPhone 3GS can offer Bluetooth and USB connections.
Using a Personal Hotspot is pretty easy once you've got it set up. It requires an iPhone with an active data plan, as well as the tethering option added to that plan (this can be added to your plan via your online account with your phone company; it usually adds at least $20/month to your bill).
To begin setting up your Personal Hotspot, tap on the Settings icon on your homescreen (unless you've moved it elsewhere; if so, locate it there and tap on it). In iOS 6 or lower, tap on General, then tap Network.
In iOS 7 or higher, the process is a bit simpler. After tapping Settings, simply tap Personal Hotspot.