When your brakes are making a loud grinding sound when you press on the pedal, this is almost always caused by contact of the rotor disc with part of the caliper. This is usually because of extreme wear to the brake pads or rotors. A foreign object in the brake mechanism can cause expensive damage.
Most likely your brake pads /shoes are completely worn out and the sound you hear is the metal brake pad /shoe backing plate grinding against your rotor/drums. Your stopping ability is severely compromised and the vehicle needs to be repaired immediately.
Squeaky, screeching or grinding brakes. It is not just embarrassing, it could be dangerous. It could mean your car's brakes need work and worse, your safety could be at risk. The problem is, even though, your brakes are making some sounds, it may still stop ok .
In general, rotors do not need to be replaced until about 70,000 miles. Both pads and rotors may need to be replaced at this mileage point, and as a general rule, they will need to be replaced in pairs.
Further driving could damage the brake discs or drums. Grinding brakes are caused by excessively worn brake linings; when the lining wears off, the metal part of the brake pad or brake shoe contacts the brake disc or drum and can quickly ruin the most expensive mechanical parts of the brake system.