PX4 Seminar provides an overview of the PX4 Autopilot system, its main software modules, and the Pixhawk hardware. It discusses the open-source nature of PX4 and lists the steps to build and flash the firmware onto Pixhawk boards. Key aspects covered include the independent and open-source nature of PX4, its main software components like the flight stack and middleware, and the hardware specifications of the Pixhawk board.