Rail-guns operate on the principle of magnetic propulsion, similar to solenoids. There are various types of rail-guns, with both simple and complex designs available for enthusiasts. Resources like scitoys.com and powerlabs.org provide detailed instructions and insights into building rail-guns. The discussion highlights the excitement around creating these devices and encourages exploration of related topics, such as cannons. Overall, the conversation emphasizes the educational potential and engineering challenges of building rail-guns.