Why change your own brake pads?

You will be pleasantly surprised to find that you can change your car's disc brake pads quickly, easily, and without specialized tools. Doing it yourself also will save you a lot of money. But even if you're not interested in doing this yourself, knowing what's involved makes it easier to understand what your mechanic may someday tell you.

Nearly all cars these days have front disc brakes. Front brakes usually wear out more quickly than the rear brakes (which could either be disc or drum brakes), so they need to be changed more often. You need to change brake pads when they get too thin, especially if they begin to make a persistent metallic squeaking or grinding noise when you press the brake pedal. But noise alone isn't always the best indicator, so it's best to anticipate when this will happen by periodically inspecting the thickness of the brake pads.

Note: If the front end of the car vibrates when you apply the brakes, your brake rotors may be warped. If the rotors appear grooved or uneven, they may be scored. In either case, the rotors may also need to be replaced or "turned" on a brake lathe, a procedure not covered here. You may need a professional's help for this, but you can see what's involved in a rotor change by looking here.

From：https://www.edmunds.com/how-to/how-to-change-your-brake-pads.html