When iPhone X was released, it introduced a few swipe gestures to replace the Home Button. With iOS 12, Apple has brought similar gestures to iPad. If you have VoiceOver enabled during the update, you will get an introduction to these gestures, with a note on how they work and how to use them. As this has never been done on iPad before, though, and as many users are accustomed to the way iOS has worked for years, I wanted to take the time to explain the changes in detail.
The basic idea is this: you take one finger, place it on the very top or bottom of the screen, and slide it toward the other end. If you're on the top, you slide down; if you're on the bottom, you slide up. You have to start from the area very close to the top or bottom edge; too far from that and iOS will assume you're just touching the screen like normal, not trying to perform one of these new commands. You'll know if you've started in the right place by the special sound iOS will make. This same sound, at higher pitches, is used to indicate what will happen during your swipe. The first instance of the sound--heard when your finger lands on the right place--is the lowest-pitched of the three iOS will produce. If you start this gesture accidentally, or decide partway through that you don't want to complete it, just slide your finger some way left or right. You can also leave your finger in one place for a moment. This cancels the action and returns you to normal, with VoiceOver speaking what's under your finger.
Let's start with the bottom of the screen. It may be easiest to find the bottom edge of the whole unit and slide up from there, as knowing where the touch-sensitive portion of the glass begins can be a bit tricky. Once you hear the first sound, keep moving your finger up. A little way along, you should hear a second sound, pitched a little higher than the initial one. If you lift your finger now, your iPad will go to the Home Screen. If you instead keep moving your finger toward the top of the screen, you will hear the third sound, pitched highest of the three. Lifting your finger now will bring up the App Switcher. Remember to move relatively straight up, as going too far to one side will cancel. It is also important to move your finger relatively quickly.
Moving down from the top of the screen is similar. Find the starting point by touching the top of the screen, on or above the status bar, until you hear the lowest of the three sounds. Slide your finger down. At the second sound, you can lift your finger to open the Control Center. At the third and final sound, lifting up will open the Notification Center.
How do you remember which is which? After all, Control Center has been a swipe up, not down, since its introduction. One suggestion is to think that, since the Home button goes home and activates the App Switcher, swiping up from where the button is will perform those same tasks. As to their order, "home" has less letters than "app switcher", so is shorter. Thus, a shorter swipe is needed to activate it.
The centers are a bit easier. Once you get it in your head that both of them are now swipes down, not up, just think alphabetically (apologies to our readers who don't use English as their first language.) "Control" comes before "notification" in the English alphabet, so the Control Center is the first one you'll activate. The word length trick will also work here, as "notification" is the longer word and is also the one that needs a longer movement to open.
What about the Dock? It used to be invoked with a two-finger swipe up, but iOS 12 has removed that command entirely. Don't worry, you can still access it, though the gesture is a bit odd. Slide a finger up from the bottom of the screen, then, after you hear the first tone, slide the finger back the way it came. If you think of a similar motion to a two-finger scrub, but done with one finger and moving vertically, that may help. A comment on this guide suggested thinking of a fast swipe up, then back down, like swiping vertically to use the rotor just after moving your finger up a bit. Whatever trick you use, the gesture itself is very easy--much easier than I'm mak9ing it sound. I actually prefer it to the two-finger swipe. There's even a new sound that plays when the Dock appears, letting you know the command worked even before VoiceOver says anything.
Finally, a note on legacy commands. As of now, the three-finger swipes from the Status Bar still work. However, no one knows how long they will stick around. My recommendation is to try to get used to these new commands, if possible, in case Apple removes the old ones in some future release. That said, commands from braille displays and external keyboards seem unaffected, so if you rely on such input methods over the touch screen, you should notice nothing new.