Feel the water!
When we enter a water environment initially it is very important to focus on relaxation and feeling the water. For a complete beginner this is not always easy and it's very natural for them to feel nervous of this new sensation.
So the first few lessons are taken very slowly so that the beginner gains confidence in their own time. The teacher will show various exercises to help with relaxation by demonstrating the water's way of supporting the body by floatation. Once the beginner is shown, through these exercises, that they are not going to sink their confidence in the water begins to build rapidly and so easing the initial fear they had.