The BehavePlus fire modeling system is a computer program that is based on mathematical models that describe wildland fire behavior and effects and the fire environment. It is a flexible system that produces tables, graphs, and simple diagrams. It can be used for a host of fire management applications, including projecting the behavior of an ongoing fire, planning prescribed fire, assessing fuel hazard, and training. This report documents the BehavePlus design and features to help users better understand the system and use it more effectively. It is based in part on material in a series of self-study lessons that were developed to provide a detailed, step-by-step description of various aspects of BehavePlus. This report supplements two reference guides on BehavePlus: a User's Guide describes operation of the program and can be accessed at https://www.fs.usda.gov/treesearch/pubs/5488, and a Variables paper describes the more than 180 variables in Behave-Plus and can be accessed at https://www.fs.usda.gov/treesearch/pubs/30565.