An interactive simulation of a transmission electron microscope (TEM) called TEMGYM Basic is developed here, which enables users to understand how to operate and control an electron beam without the need to access an instrument. TEMGYM Basic allows users to familiarize themselves with alignment procedures offline, reducing the time and money required to become a proficient TEM operator. In addition to teaching the basics of electron beam alignments, the software enables users to create bespoke microscope configurations and develop an understanding of how to operate the configurations without sitting at a microscope. TEMGYM Basic also creates static ray diagram figures for a given lens configuration. The available components include apertures, lenses, quadrupoles, deflectors and biprisms. The software design uses first-order ray transfer matrices to calculate ray paths through each electron microscope component, and the program is developed entirely in Python to facilitate compatibility with machine-learning packages for future exploration of automated control.