When you apply pressure to your car’s brake pedal, brake fluid pressurises to the caliper pistons on each wheel’s hub. This forces a brake pad to press against both sides of the brake disc, which turns together with the vehicle’s wheels. This friction slows the car and ultimately brings it to a stop.
In time brake pads will wear out and will need to be replaced, so continuing to drive with worn out brake pads is extremely dangerous. There are few telltale sign to worn brake pads: if they are wearing unevenly then it can cause the car to swerve under braking, and it can also be indicated by squeaking and screeching as well as a reduction in stopping power.