Current developments in integrated photonics require the design of new integrated structures and the execution of multiple optimization cycles, for which accessible and flexible modeling techniques represent essential tools.Commonly used in engineering for modeling complex systems, transfer matrices are simple and powerful tools that may be implemented for the simulation of circuit-and system-level photonic elements.In this tutorial, we present a detailed description of a modeling methodology based on signal-flow graphs and transfer matrices that successfully predicts the spectral behavior of resonant photonic circuits.Every stage of the modeling process is comprehensively elaborated in the tutorial, with the aim that it serves as a starting guide for new researchers in the field.Validation results are presented for demonstrating the accuracy of the model in reproducing published benchmarks, and several studies are carried out to illustrate model's scope.In addition to the basic theoretical and practical considerations required for the construction of photonic circuit models, an open-source Python-based software is provided, enabling the immediate implementation of described techniques and their use as baseline for advanced studies and designs.