Week 01 - Assignment 02 - Exercise 01

I don’t understand the Assignment 02 - Exercise 01.
Model is HappyModel()
I am a bit confusing here, the HappyModel does not have any input.
My question is: should I add some input such as Happymodel(x1, x2, etc.) for the model to work, or just leave it alone as this is no input model?

Thank you

The input to a Sequential model is applied later, in the cell that calls the model.