In Simulation you use computers or simple models of what you're trying to create or study. for example MATLAB software is a very powerful simulation tool. you can create a full communications system or a car suspension system by computer, studying and experimenting it, without a real car or system.
when you are trying to create a real system the process is called implementing. imagine you've designed a program to do something on a microcontroller. by simulation you know what that program can do without even working with it. but in real world you implement the system you've simulated by buying a microcontroller and programing it. that's the difference.
simulation is almost cost and risk free for studying products. because it's all in computer. when you get the result you're expecting from simulation you start implementing your product on a real system.