A model is a simplified representation of reality. It establishes a link between theory and reality, and makes a concept concrete. Models are used to educate, demonstrate, and inspire enthusiasm for further research. They allow scientists to experiment, make predictions, or test hypotheses.
Working with models has both advantages and disadvantages. In the real world, you need to consider exceptions to the rule and coincidences. In a model, however, you have a higher level of control over these unknown factors.
Moreover, as they represent the real, changeable world, models can never be complete or finished. That is why researchers have to take into account they cannot simply translate results they gain from models into reality.