The Show Me / Tell Me questions are designed to test your ability to maintain basic elements of your vehicle.
The new test (from 4th December 2017) has 14 questions in the tell me questions which will be asked at the start of the test once the number plate has been read.
The shpw me questions will be asked on the move - don't worry if you can't answer the question straight away as they all start with the phrase - 'when it's safe can you show me...'
You cannot fail on the questions, however if you lose control of the car in trying to show the examiner the answer then this can well become an issue. Practice is definately necessary.
Some of these questions are quite easy and obvious, other require effort in learning the correct phrasing.
For further information on the test change see my blog on the subject.