If you hear or feel a grinding when you apply the brakes, the pads are definitely gone and the rotors are gouged by the metal pad backing plate. You waited too long for a cheap brake job and a simple pad replacement. You will most likely need to replace the rotors as well. If they are not too badly grooved, you could have them turned (resurfaced) for about $5-$7 each. Or, for $19.99 each, you can get new rotors and for about $35, you can get Performance Friction Carbon Metallic 4214S pads with lifetime replacement gaurantee, both from AutoZone.
For tools, you will need a Torx 40 socket to remove the caliper pins and a C-clamp or caliper spreader to compress the piston. You should apply silicone grease to the cleaned slider pins and torque them to 25 lb-ft during reinstallation. Cut and bend a coat hanger to hang the caliper from the spring while you replacing the rotors.
