Cardio is cardiovascular exercise. To get Cardio working and know its happening is when the heart is pumping fast and flows more blood in your system, which carries nutrients and oxygen to cells. Any exercise can work like running, Biking, basketball, skateboarding which is what I like to do. Many don't like to do it because they get exhausted, sweaty and or just to lazy to do it but it would worth to do. To get cardio working and pumping the heart could only take a few minutes depends on the exercise you start off with. Doing cardio is good because it helps you lose weight and also burns more calories.
One cardio activity that always works you out is running/jogging which works the heart out a lot. This is one of the best because doesn't involve any equipment just a pair of shoes and your good. Running is also good to start losing weight because its easy just takes time and also burns lots of calories. Running for about 10 minutes around the block from your house can change a lot making the heart pump a lot. When its not working you out is when you slow down and stop running. Another cardio exercise is basketball. This is a good one because it involves shooting, passing and running up and down the court for a long time. It is impossible to not get cardio because even if you don't run down the court you just have to walk which also pumps the heart.