Guide to the Keras functional API, Keras Team, 2024 (Keras (official documentation)) - Provides a detailed explanation of using keras.Input and the Functional API for model construction.
Guide to the Keras Sequential model, fchollet, 2020 (Keras) - Explains how to use the Sequential model, including the input_shape argument for the first layer.
Deep Learning with Python, François Chollet, 2021 (Manning Publications) - Written by the creator of Keras, this book covers fundamental Keras model building, including input definition. (2nd edition)