There are several good internet sites that have tutorials for building STELLA models. Use them to help you develop your own model. Expect your model to grow and change as your understanding of the problem changes. You should be thinking about your problem statement and trying to adjust your STELLA model so it answers the question and supports or refutes your hypothesis. Here are links to three sites that will help you understand how a STELLA model works. Look at the model and the mathematical equations within the models.

Introduction to Stella by Shodor
Shodor Simple Stella Model
Generic Stella Models

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