How to decide number of Layer and Units

week 1
Classroom: https://www.coursera.org/learn/advanced-learning-algorithms/lecture/vYsrR/inference-making-predictions-forward-propagation

At time: 1:13 It said that here Using 3 hidden layers, 1st layer has 25 units, the second one has 15 units, the last one 1 unit

My question is how to decide :
How many layers Do I need?
And for each layer How many Units do I select?

Experience and experimentation.