This graph demonstrates how a computer can iterate a rate equation. You can push the "iterate" button to see how the population of rabbits increases with each year. Also you can change parameters, the number of rabbits in a litter and the number of rabbits in year 0.
Notice how changing the different parameters change the graph. What does changing the number of rabbits in the year 0 do? Use the "iterate" button to see how the population becomes enormous after some years.
Once you understand you this simple model works go on to the more complicated SIR model