How do I split screen, to work on different apps?

Follow the steps here: Use Multitasking on your iPad - Apple Support

Do note, not all apps support spit screen.

Take a look at these Apple video guides:

https://www.youtube.com/watch?v=ITzy5J3j5Is

https://www.youtube.com/watch?v=nSBZKr5kXYM

After viewing, you’ll be ready for the additional Multitasking Guide:

https://support.apple.com/en-us/HT207582

Here are links to both the online and downloadable versions of the User Guide:

https://support.apple.com/guide/ipad/welcome/ipados

https://help.apple.com/epub/ipad/en/

I hope you find these materials to be helpful in resolving any issues that you may be experiencing.