does deploy script in sandbox means it will deploy to production? or it will update the existing script with the changes?

If you deploy a script in sandbox, that deployment is ONLY in sandbox. You would need to do the same process in production.

so basically deploy means updating the script in sandbox only if am doing it in sandbox? Thanks a lot for your help.

Yeah it should only be sandbox. You have to explicitly deploy things to accounts.

Thanks again. When I try to deploy and in Applies To I try to select Sales Order i dont find this option and i can see the previous deployment has been done on Sales Order.