Why my iPad screen is split in two different parts of screen.

You may find these overview Apple video guides to be helpful:

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

Use Multitasking on your iPad - Apple Support

The iPad User Guide for iPadOS is also a rich source of information. Here are links to both the downloadable and online versions of the Guide:

‎iPad User Guide on Apple Books

iPad User Guide - Apple Support

I hope this explanation and additional information is helpful in resolving any difficulties you may be having with Multitasking features of your iPad.

Is sounds like you are using Multitasking. See this link --> Use Multitasking on your iPad - Apple Support