What is a model? what is a decision?

Can anyone (if at all possible) please explain and discuss the modeling process in about as much detail as you can. Thanks and god bless for the help or info anyone can give ;) PLEASE is there anyone that can help me cause I rlly need it, plz plz plz anyone!!!

P.S. This question is in relation to system modeling theory, in case anyone didn't know the topic, thanks again.

A computer model is an attempt to simulate real life events using data from similar events in the past. Most often the purpose is to predict those events in the future or for training. They are used for many different purposes like weather prediction, technical guidance for investors and military training.

Some models go a step further and output decisional information when certain parameters in the model are met.

Example: An investor enters historical stock price data into a computer and runs different statistical algorithms to find where the numbers were in the past when the stock turned up and when it turned down. With that information, they could electronically monitor real time prices and make trading decisions when the current data meets the same criteria. I'm not suggesting you can make money that way, just using it as an example.