Top view
The most basic view, and the easiest one to design in. You see the pool from above. Pinch with two fingers to zoom in and out.
3D view
Move around the pool. Pinch to zoom, and use one finger to turn the camera and look at different elements.
Live view
Use this one when you place the pool in the garden of your customer. See the tutorial Using live view / augmented reality for how it works.