A Byebug developer works with Ruby programs, employing the Byebug gem to debug code. They utilize the Byebug tool to pause execution at certain lines or conditions, inspect variables, track execution flow, and modify code on the fly. They navigate through the codebase using step, next, finish, and continue commands. They also evaluate and manipulate the program state, enabling them to find and fix bugs. Additionally, they use advanced features like thread and post-mortem debugging. Essentially, a Byebug developer uses this powerful tool to enhance the efficiency, reliability, and quality of Ruby applications.