Brake pads and Brake Shoes typically last from 50,000 to 70,000 miles before needing replaced.
For brake pads you can check through the vehicles rims spaces and look at the brake pads and there should be at least a 1/4" thickness to the brake pads and if not then they need replaced.
For brake shoes you really can't tell unless you remove the brake drums to inspect them unless you hear some metal upon metal scraping or when the brake pedal goes further to the floor than it normally would.
Sometimes you may need to jack the cars wheel up and remove the wheels to inspect the brake pads better.
Brake pads also contain a metal strip that is supposed to scrape against the brake rotors when the brake pads have worn down too much to not be safe.
Some brake shops will also perform a free brake inspection if you're unsure about how to check the brake pads or have a way to check them yourself.