When you're demonstrating an iPhone app to someone else, or just want to quickly share something you've seen online, screenshots are a great way to get the job done. They're also handy when troubleshooting your device or helping out a friend with theirs, as they make it very easy to capture images of any part of your screen.
Regardless of which model of iPhone you have, taking a screenshot is as simple as pressing two buttons at the same time. The first button is the side button or power button, found on the right-hand edge of your phone (iPhone 7 and earlier) or the top of your Home button (iPhone 8 and later). You'll know the screenshot worked when the screen flashes white and you hear the camera shutter sound (as long as your iPhone isn't in silent mode).
Once a screenshot has been taken, a thumbnail temporarily appears in the lower left corner of the iPhone's display. Tap it to open the Instant Markup interface where you can crop, add text or a signature, draw arrows and shapes, and more. If you don't want to edit the image, simply swipe the screenshot away and it will disappear from your iPhone.
After you're finished editing a screenshot, you can save it to your Photos library or send it to Message, Mail or other apps. To see a list of your saved screenshots, go to Albums > Screenshots. You can also view a PDF of any screenshot by opening the Photos app and tapping Files > Print & Export > Print Screen.