In this lesson, students learn about Venn diagrams, which are illustrations using circles or shapes to show relationships and differences between various sets of information. The teacher provides a practical example involving pet preferences, demonstrating how to represent data on cats and dogs using Venn diagrams. Students are guided step-by-step on creating these diagrams, allowing them to visualize and understand the data better, including the number of students who prefer each type of pet. Overall, this interactive approach helps solidify their understanding of data representation through Venn diagrams.