Replacing cables is a good job to start with. You will probably mess up a few cables while you are learning. Go to Price Point or Bike Tools etc and order a few of each, brake and gear. Get the stainless pre-stretched or die-drawn type. Maybe $3.00 each and nicer than what the LBS carries. Some ferrules and end tips are good to have and maybe some little o-rings for the rear brake cable. Follow Park Tool instruction step by step for adjusting your gears.