Ideally, your car will start to slow down as soon as you press on the brake pedal. However, if the brake pedal is broken, there is a chance that it will go all the way to the floor before anything happens. Typically, this component will become defective or broken because it is old or because you tend to hit the brakes too hard.
Over time, parts such as the master cylinder or brake booster can become worn and less responsive. These are important parts that should be repaired or replaced as soon as you start having problems with them.
There is also the possibility that air or fluid has gotten into the brake line. If a fluid leak has occurred, you will likely need to replace the line entirely. However, an air leak may be remedied by bleeding the line during a service appointment.