Unless they have changed it since last year, your salesperson needs some more training. "B" is for braking, and it is useful when going down long slopes... similar to taking the overdrive off on a regular auto transmission. It doesn't seem to affect mileage much if any. I sometimes use it around town when I want more "engine" feel.
Also, after about 6 months, you won't be watching the monitor anymore. It is good in the beginning to help you understand how things work and to get you used to feathering the gas. Oh yeah... it is cool when you give rides to others too.
To use the battery more, you just use less gas pedal. It is surprising how much you can raise your foot and still maintain the same speed. The car is a hybrid, therefore you cannot run on the battery alone by choice. The computer decides what you need based on speed, position of gas pedal, temperature, current charge levels, etc.
One thing that really freaked me out at first was the inability to rev up the motor in neutral. You can push the pedal all the way down and nothing happens. I have also gotten used to just turning the key on quickly, then letting the car start itself. When I do the same in my other vehicles, and I just sit there wondering why the engine doesn't start.
I hope you'll be as happy with your purchase.