My Car Jerks When I Step On The Brakes. What Can I Do?

If it jerks as in grabs and releases dependent on how you "step" on the brakes it will most likely be the ABS along with fresh pads. Fresh pads are always a little bitey than normal but that will change once they've been worn in.

ABS will cause the brake pedal to pulse fairly rapidly if you do trigger it.

unlikely it's a leak from the MBC as a loss in brake fluid would cause spongy braking (hard pressing on pedal but minimal stopping)

Describe the "jerk" more and you should be able to get a better answer

Well lets see have the brakes checked asap and check your cvc boots for cracks and tears look for lots of grease mainly look at your brakes even the brake fluid could cause a problem mainly a pull is a bad caliper could cause an accident if not looked at I had that happen once master cylinder was cracked caused me to leave the road...

I am not a mechanic.

Could be any number of problems with the brakes.  Maybe the anti-lock brake system since they pulse on and off to avoid skids.
Bad rotors or caliphers.
Brake fluid leak at master cylinder, other leaks anywhere in system.
Also, a car that doesnt idle properly may buck as it comes to a stop when it depends on the idle mixture to keep the engine running but you should notice the rough idle or stall when you stop.

I can almost guarantee its warped rotors you can either get them shaved or replaced