Press the Side button and the Volume Up button at the same time
Release both buttons quickly
Tap the screenshot preview to edit it
Tap Done to save or delete it
Find the screenshot in the Photos app under Screenshots
Use AssistiveTouch if you cannot use the buttons
Go to Settings, then Accessibility, then Touch, then AssistiveTouch to enable it
Tap the AssistiveTouch button, then Device, then More, then Screenshot