Riding the brake

P means Park. Put the shifter here every time you walk away from the vehicle. It is using the gearbox as a parking brake.It will roll a tiny amount as the park gear catches into position, but usually no more than the width of your foot. It doesn't matter if the engine is running or not.
R means Reverse. This is the position you use to make the vehicle go backwards.
N means Neutral. The Vehicle is NOT in gear so if left on a slope without the parking handbrake, (E brake), ON it will roll away.
D means Drive. This is the position you use for general everyday driving. It lets the engine use the whole of the gearing range.
S means Sport. This alters the setup in the gearbox to give the vehicle a slightly higher performance compared to the 'D' position.
B means Braking. More correctly called 'Engine Braking'. This is the gear you use if you are going down steep hills. Note some companies use 'L' instead of 'B'. It usually means Low, as in low gear.
It uses the gears in the transmission to create drag on the engine which acts as a braking effect. It helps prevent you 'riding' your brakes on really steep downhills. If brakes get too hot they don't work as efficiently.

you can if you ride the brake --city driving with lots of traffic will wear down brakes --if brakes become damaged

The way to avoid this when parking the car on a hill is to apply the parking brake first, allow the car to settle in position by easing off the regular brakes, then put car in park. When it is time to go put the car in gear then release the parking brake. Let the parking brake do all the work. This problem is common to most cars with an automatic transmission. The weight of the car is pressing against the parking mechanism inside the transmission. Many folks have to resort to having a friend rock the car forwards and back to free up the parking mechanism.

you can't estimate brake wear with mileage, dirver style, conditions such as highway, city, hilly country, all have a different effect on brake wear, i have seen some drivers only get 15,000 miles and others over 100,000, best to get them inspected once a year and replaced when 60 to 70% worn

look up under feet area brake peddal has a switch hooked to brake peddal could be bad switch or something catching it! good place to start!