Bitcoin transactions are irreversible.
This basically means that you can't take back the same bitcoin you send to someone unless they themselves send it back to you.
This is there to stop fraud from taking place because in bitcoin's system there is no need for a trusted third party. For example, if you go to a store and buy something with bitcoin, you can't reverse the transaction after you leave the store.
Remember that the best way to understand Bitcoin is through its Whitepaper.
Bitcoin's Whitepaper published by Satoshi Nakamoto in 2008 is fundamental to understanding bitcoin and blockchain technology. If you want to learn about bitcoin in simple terms and understand the bitcoin whitepaper in urdu/eng, This is one of the best sources:
https://www.youtube.com/watch?v=VmusvimRKWkHope it helps!