Here’s how you do it.
Start by writing your message on your iOS 10 iPhone or iPad (more or this later), just like you always do. Then, instead of tapping the the arrow-in-the-blue-circle “Send” button, hold that button down (you might have to press hard– depends on whether you have an iPhone with 3D touch, and on your 3D Touch settings. Settings/General/Accessibility/3D Touch).
That leads to choices:
You can play with the “Bubble” options and figure them out right away. But we’re talking about Screen Effects here, so tap the big “Screen” button at the top. When you do that, you see an animated preview of the Balloons effect. You can use Balloons right away (just tap the arrow-in-the-blue-circle “Send” button), or swipe from right to left to see the other choices (Confetti, Lasers, Fireworks, and Shooting Star) to choose one of them, and then tap the arrow-in-the-blue-circle to send.
Make your choice, then tap the arrow-in-the-blue-circle “Send” button. Or tap the x-in-the-grey-circle to cancel. That’s all there is to it.
Make a website! Sign up with Fatcow and get super-affordable web hosting, plus WordPress. Fatcow is my first recommendation when people ask for a web host. Check 'em out, and tell them I sent you!
UPDATE: iOS 10.2 brings two new screen effects– Love, and Celebration. Have a look and give them a try.
Note: Screen Effects only work with iOS 10. The sender’s iPhone (or iPad) has to be on iOS 10, and the recipient’s iPhone (or iPad) has to be on iOS 10 too. If you try to send screen effects (or bubbles) to any other device, the screen effects won’t show up (although the message does go through, and a notice– “Sent with Balloons”– will accompany the message). The effects also don’t show up on a Mac, and you can’t send them from a Mac either, at least not yet. By the time you’re reading this, things might have changed for the better.