You're off on a bike ride. To stay safe, just as you set off you check the brakes. A bit squeaky, but squeezing the brake levers changes your motion.
When you squeeze the levers, many complicated things happen. Some squeezing, some slipping, some gripping — you could imagine forces(pushes and pulls) all over the place. But physics likes simple, and here is how. First re-imagine the rider and cyclist:
You want the brakes to slow bike and rider down: everything in physics-world above (did you notice that you've also isolated the bike and rider: the road, the hedges, the traffic are all gone.
You could imagine other ways of slowing down — coasting to a halt, riding into a hedge or perhaps something less forgiving for an even more sudden stop.
Every one of these slows you down. And in every case a force changes your motion.
You could also take a street-level pair of snapshots of your journey:
Only a force acting on you and your bike can slow you down. Just think of trying to stop on ice.