In the video, a person is using a green suction cup to clean the glass of an aquarium. The aquarium is filled with water and has plants and rocks inside. The person is holding the suction cup with one hand and using the other hand to move it across the glass surface, removing any dirt or debris. The suction cup appears to be effective in cleaning the glass as it leaves a clear path behind. The person continues to move the suction cup back and forth until the entire glass surface is clean.