how could i get back the money?
Bitcoin transactions cannot be reversed, cancelled or undone.
[I transferred] my bitcoin to someone I really don’t know
If you have contact details for the person, you can ask them if they are willing to create a new transaction to send some money back to you.
If you only know a Bitcoin address, you cannot get contact details from that address. A bitcoin address does not identify a person, a place or a business. It is just a number, effectively a random number.