If you just want to be able to run for a long time, then all you have to do is practice running for longer and longer periods of time. If you want to run a specific distance and increase your speed, then you would do the following...
example:
Goal: Run 3 miles in under 24 minutes.
1 mile time is 8 minutes.
Run a mile. Rest 10 minutes. Run a mile. Rest. Run.
You will have run three miles in 24 minutes. Next training session, reduce rest time between miles. Eventually you should be able to get it down to 3 miles in 24 minutes without rest.
The more specificity you have with your cardio goals/training, then the more effective you'll be.
