To demonstrate the difference between answering true, false or not given, I usually show my students some easy examples from a General Reading exam.
The following examples come from Cambridge IELTS 7, pages 119-120.
1. The entrance to the campsite is locked after 10 p.m.
2. No dogs are allowed on the campsite.
3. You are not allowed to cook food on open fires.
Don't make any noise after 10 o'clock at night or before 7.30 in the morning. Dogs must be kept on a lead. Owners of dogs that disturb other campers by barking through the night will be asked to leave. The lighting of fires is strictly prohibited.
Decide whether the question statements are true, false or not given. Then try to explain what we can learn from this exercise about the differences between true, false and not given.