Iknow I need a new overflow tube but I don't know if it comes with a kit or I can purchase it alone. I've never worked on toilet repairs before.

Go to any home depot or Lowe's and you can buy it as a kit or only the tube, open the attach link will show you how to replae it, Thanks

John

Video: How to Replace a Toilet's Overflow Tube | eHow.com (http://www.ehow.com/video_5116754_replace-toilet_s-overflow-tube.html)

Iknow I need a new overflow tube but I don't know if it comes with a kitWhile the sell rebuild kits for the toilet tank this is not what you're looking for. Ask for a "flush valve", a spud wrench and a spud washer,(see images).
Shut the water off at the angle and sponge the water out of the tank. Remove the tank bolts and pull the tank clear.
Remember which way the flush valve set in the tank and Using the spud wrench remove the old valve and install the new one. Replace the spud washer and reinstall the tank and connect the supply. Good luck, bTom