The answer to 'how to kill rat' is to use humane traps or hire a professional pest control service. Rats can carry diseases and cause damage to your home, so it's important to address an infestation properly. Avoid using poisons or other harmful methods, as they can be dangerous for pets and children.
If you decide to use traps, place them in areas where you've seen rat activity, such as along baseboards or near food sources. Check the traps regularly and release any caught rats in a remote area away from your home. For a severe infestation or if you're uncomfortable handling the traps, it's best to call a professional pest control technician who can safely and effectively eliminate the rats.