The Apple iPad has two models; one offers 3G and Wi-Fi, and another that offers only Wi-Fi, to access the Internet. If you purchased an iPad that only offers Wi-Fi, you may tether your iPad to your iPhone to access the Wi-Fi tethered from your iPhone. You must have a tethering plan through AT&T to activate tethering from your iPhone though. Once you have set up a tethering plan for your iPhone, you will be able to tether your iPad.
Tap the "Settings" button on your iPhone.
Tap on the "General" button on your iPhone.
Tap the "Network" button on your iPhone.
Tap "Internet Tethering" on your iPhone.
Tap "On" to turn the tethering option on.
Tap the "Settings" button on your iPad.
Tap on the "WiFi" button on your iPad.
Tap on your iPhone when it appears under "Choose a Network."