How can o do a screenshot on the iPhone 7

jdrppr ~ See this Apple Support Article:

Take a screenshot on your iPhone

...found by searching Apple's Knowledge Base.

And there's a way to take a screenshot with just a tap rather than pressing physical buttons:

Use AssistiveTouch on your iPhone, iPad, or iPod touch

To turn off: Settings > Accessibility > Touch > AssistiveTouch = Off

You'll wish you'd made this simple iPhone tweak years ago

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Hello,

To perform a screen shot you need to press the Side Button power button, and the home button at the same time. You will then have to release both of the buttons within a second. A thumbnail of your screenshot will appear in the bottom right of your screen, you can tap to view the screenshot and crop it, or swipe it off to your camera roll.

Hope this helps!

Brad