Open the Settings app on your iPad.
Navigate to Accessibility.
Scroll down and tap Guided Access (under the General section).
Toggle Guided Access to ON.
Tap Passcode Settings and set a passcode.
Optional settings you can configure:
Open the Tap For Good app on your iPad.
Triple-click the Side button (or Home button on older iPads).
Tap Start in the upper-right corner to begin Guided Access.