The first major difference every new iPhone X owner will notice is the lack of a physical Home button. Muscle memory will keep many people tapping a non-existent button, at least for a few days before they get used to swiping up. For those who prefer tapping a button, there is a work around - you can create a virtual Home button using iOS's Assistive Touch feature found in the Accessibility settings. Here's how to do it on iPhone or iPad:
Indeed, because of the "notch" there is less room at the top of the iPhone X screen to show information. Battery percentage was a casualty of this, along with the alarm clock, Bluetooth and a few other symbols. However, you can still view these in your Control Center. Just drag down from the top right corner to see your battery percentage.
You can make an Emergency SOS call on iPhone X the same way as before, by rapidly pressing the side button 5 times. To do this it must be enabled in Settings -> Emergency SOS, where you can toggle "Call with Side Button." It should be toggled on by default. You can also make an emergency call by pressing and holding the side button and either volume up or down until you see the power down screen appear. You will see a slider to make an Emergency SOS call.
The flashing "double click" instruction has fooled many first-time iPhone X users, causing them to awkwardly start tapping the screen. What it is trying to tell you is to double click the side button, which will invoke Face ID to make sure you have permission to download apps. This is simply to avoid downloads due to accidentally tapping the "Get" button and then having Face ID automatically give permission to download because it sees you.
To force quit an app on iPhone X, open your App Switcher by swiping up from the bottom of the screen halfway then pausing, or turn your swipe to the right when you reach mid-screen. Find the app you want to kill then long press on it until a red "-" button shows up in the top left corner of the app. Tap it to quit the app.