I use one foot, like driving a manual, but some argue one foot per pedal is safer.
NEVER you your left foot for braking, it is highly dangerous!
I have worked in the motor industry for all of my working life and I can tell you that in general, cars are not designed for left foot braking.
Why do you suppose there is a footrest, located to the left of the footwell, to rest your left foot on?
Why would you attempt to learn to drive, differently to 99.99% of all other drivers?
There is simply no advantage in learning to drive in that manner and at least two reasons why you shouldn't.
1. Generally speaking you left foot is 'conditioned' over many years, to push the pedal to the floor.
Can you imagine what would happen in a panic situation if you were to attempt to push the brake pedal to the floor?
2. You could easily have a situation, where again in a panic, you attempt to push both pedals at the same time, which would result in the engine is 'fighting' the brakes. not a good idea and of course not possible using just one foot!
Learning to drive an automatic car, using both feet would inevitably result in you finding it impossible to drive a manual car, should you wish to, at some point in the future.
I can't imagine any driving instructor advocating the use of both feet to drive an automatic car.