Anyone can explain simulation for uncertainty in more simplely way?

I read Kaplan . Sensitity analysis considered the effects of changing one variable at time while the sitimulation( Monte Carlo Sitimulation) improves this by looking at many changing variables at one time. it produces a distribution of possible outcomes from the project then the probality of different outcomes is then calculated. These is done in 3 stages:
1- Specify the major variable e.g market details where the market size, selling price , market growth rate will be looked into
2- Specify the relationship between the variables to calculate NPV
3-Simulate the Environment- This now forming the distribution for each variable – the select the value of each variable corresponding with the selected random nmber and compute the NPV- This process ir repeated so many times to create a probability of distribution returns

the result of a simulation exercise will be a probability of NPVs

i think this will help you