One of iOS 8's most talked about features is Interactive Notifications. Now when a notification banner or alert appears, a response can be sent off without leaving the current app or unlocking the device. This works right out of the box with Messages and soon with many other apps as developers push updates for iOS 8. How to take advantage of this new feature is fairly intuitive, however it took a bit of experimentation to fully understand how they work.
The best example of how Interactive Notifications work is with Messages. When your device is unlocked and a message banner comes in, simply pull down on the banner and you'll be able to send a response without leaving the current app. The only thing to be aware of is that any follow-up messages will not be shown to you, which is especially important to know if you're responding to someone who likes to send multiple messages in a row.
If you miss the banner, you can still take advantage of the feature. Simply pull down Notification Center and swipe from right to left on the message and tap "Reply" to bring up the quick-reply interface.
Even more handy is the ability to act on a notification right from the lock screen. Once again, swipe from right to left to reveal the notification's options. Tapping "Reply" on an iMessage will allow you to reply without unlocking your device. There's also a little round "x" which will clear the notification from your lock screen. Handy, right?
Other apps may present other options such as a pair of buttons which perform actions specific to the app. As a bonus tip, even if the app doesn't offer additional options, you'll still get something out of pulling those banners down. If the content of a particular notification is longer than what can be displayed in the banner, pulling it down will show its entire contents. Pretty cool, eh?