I have a 2001 4 runner with 45 k miles.

what are the brake parts that wear out fast ?
such as front or rear brakes, rotors.

Unless neglected, the only parts that wear out fast are the front pads and the rear shoes. The springs in the rear can loose tension, but not normally at 45K. The rotors may or may not have wear, depending on the condition of the pads. Normally, they are only slightly marked and need to be resurfaced when the pads are changed (same for rear drums).

If you are going to replace your linings, get a manual from Chilton or Haynes and do it right.