Do you fail if you cannot do the driving test manoeuvres?

Anita,

If you cannot perform any of the manoeuvres, you will fail without a doubt. During the driving test, the examiner will ask you to do two of the following manoeuvres:

1) Reversing around a corner
2) Turning in the road
3) Bay parking
4) Parallel parking

If you cannot perform even one of the manoeuvre properly, you will fail the practical driving test. Note that even if you manage to do the manoeuvre, you may still fail if your observations were poor.

I did a mock test and passed, does that mean I will do well on my practical driving test?

Passing the mock test is a good sign but it does not guarantee that you'll pass your practical. There are many reasons for that - people tend to get more nervous during the actual test and make silly mistakes, weather conditions may be different, circumstances on the road may be different, the examiner may ask you to do a route that you are not familiar with.

However, as you've passed your mock test, it shows that you know how to drive and there's no reason for you not to pass the practical driving test.