How do I stop iPad screen from going to sleep

Go to settings - display and brightness - set auto lock to never.

If you use a screen lock passcode (with touchID or faceID) you won’t see any option to set screen sleep to “never”. You would have to remove your screen lock passcode first to get that setting (no point having device lock security if you‘re going to leave it on, and thus unlocked, all the time).

FYI,

Keeping the screen on an iDevice active all the time will greatly the iDevice’s reduce battery life.