You can take a screenshot a few ways. Use the one most convenient for you.
When you’re on the screen you want to capture, choose one:
Touch & hold three fingers on the screen. (If this doesn't work, turn Use Three finger screenshot on.)

To scroll and capture more content, tap
.
To stop scrolling before the end of the page, tap STOP or
.
Do any of the following:
Open the Photos app
and tap Collections > Screenshots.