The student created an A3 poster using Paint.net. They first changed the canvas size to 29.7 cm by 42 cm. They then created different layers, including a black background layer and layers for microphones, the word "factor", and yellow stars. On the microphone layer, they drew microphones in red and white. They used layers, tools like the paint bucket and brush, and adjusting colors to design their poster for their first creative lesson.