The examiner will ask you one 'Tell Me' question at the start of the driving test before you start driving, where you'd have to explain how you'd carry out a safety task.
You'll also be asked one 'Show Me' question where you'd actually have to show them how you'd carry out a safety task while you're driving. The Show Me question could be asked at any time during your driving test including the independent driving part.
You won't fail your driving test if you get any of the 'Tell Me' questions wrong but you would get a driving fault. You can however get a serious or dangerous fault if you lose control of the car when answering the 'Show Me' question.