cardio - short for caridovascular, refers to the heart. so basically any form of training or work out which really intensifies and speeds up ur heart rate. like running, sprinting, rope jumping...u know what i mean? something thats gonna make ur heart start beating very fast and ur gonna be out of breath. lol. i know my way of describing this was funny. hopefully u get what i mean.
about ur 6 pack, well ur a guy so dont worry, if u continue with ur crunches ur gonna get it very soon, coz its so easy for men to make muscles compared to women. lucky you... and also give it time. coz ur still young...in a year or two ur muscles r gonna develop on their own anyway..and become bigger and stronger. just eat healthy..dont eat fattening things. STAY AWAY from mayonaise.. mayonaise is the enemy dude. it makes u put on so much weight. hmm what else. just stay away from junk food and fried oily things. eat carbs and some protein every meal, drink lots of water and do crunches like 3 times a day..it will work