Apple just launched the iOS 11 public beta for the whole world to try, and holy heck, don't get too excited yet. Obviously, your iPhone or iPad will be cooler than all your friends' are if you're running the new software before any of them. There will be consequences, though.
Image: Apple / Gizmodo
First off, not all Apple devices will run iOS 11. You'll need an iPhone 5s or newer, a 5th generation iPad or newer, an iPad Mini 2 or newer, or an iPad Air (1 or 2). You can also install iOS 11 on a 6th generation iPod Touch, if that's your jam. (Check out a full list of compatible devices here.)
Next, you'll definitely want to back up your old device. It's now possible to revert back to iOS 10, if your experiment with iOS 11 is too bug-riddled, but it's not exactly easy. (Check out the instructions for how to do that here.) But before you even think about installing the iOS 11 public beta, you must understand that the new operating system will be bug-riddled. Until the software gets an official release, you can expect your phone to be a big pain in the arse, featuring all kinds of new adventures like crashing apps and awful battery life. So you should consider running the new software on a secondary device, in order to avoid ruining your day-to-day phone usage.
If all this sounds fine to you, just head over to the Apple Beta Software Program page from the device you want to install the new software on. Hit "Sign Up," and then sign in with your Apple ID. Accept the agreement, navigate to the iOS tab, and download the iOS 11 software. After that, your device will open up the "Profile," and tap install until your phone reboots. Finally, when your phone boots back up, check for a new software update, and your phone will download the latest version of the iOS 11 beta.
Once you're all updated, have a blast. Impress your friends. Expect everything to crash! It will be annoying, but you'll feel so cool in your annoyance. Plus, the new software looks pretty great!