To be able to use the feature, all your devices must share the same Google account. You can then activate Instant Tethering in the Settings menu: tap "Provide data connection" to set up a host device or tap "Get data connection" to set up a non-host phone or tablet. After the initial setup, your non-host devices will automatically connect to your host devices when you need an internet connection. It's a pretty sweet deal if you're always busy on the go, since manually tethering devices all the time can be time consuming. Another plus is that your receiving device will automatically disconnect after 10 minutes of no activity to save power and make sure your tablet/phone doesn't die too quickly.