Press together the top Power button and Home Button, and instantly release as you see screen flash.
You can see the results in Photos> Albums> Screenshots
Taking Screenshots in iPhone 6, 7, and iPhone 8
You have to press Power button and Home buttonsimultaneously and release when you see a light screen flash.
You can see the results in Photos> Albums> Screenshots
How Can I Screenshot on iPhone X & Later
To capture screenshot on iPhone X and later models press Volume up and Side button together and release quickly when you see screen flash.
You can see the results in Photos> Albums> Screenshots
How Can I Edit a Screenshot on iPhone
Open the Photos app and select the screenshot which you want to edit.
Tap on the Edit icon at upper side of your screen. Now tap on Markup icon the tap on Plus icon and make changes which you like. You can add text, shapes, signature and more with this feature.
After you are done just tap on “Done” to save changes.