Venn diagrams visually represent sets and operations. Rectangular region = universal set U; circles = sets A, B, C. Regions: Overlap = intersection; non-overlap = difference; outside = complement. Drawing approach: (1) Draw rectangle (U); (2) Draw circles (sets); (3) Shade regions for operations. Applications: (1) Counting problems with overlaps; (2) Verifying set identities; (3) Solving word problems with categories. Example: 100 people surveyed. 60 like coffee, 50 like tea, 30 like both. Like at least one: 60 + 50 - 30 = 80. Using Venn: Left circle (coffee only) = 30, overlap = 30, right circle (tea only) = 20. Total = 30 + 30 + 20 = 80. Exam tip: Label regions clearly. Use inclusion-exclusion principle. Practice: Complex multi-set diagrams.