The document provides an overview of convolutional neural networks (CNNs) and their layers. It begins with an introduction to CNNs, noting they are a type of neural network designed to process 2D inputs like images. It then discusses the typical CNN architecture of convolutional layers followed by pooling and fully connected layers. The document explains how CNNs work using a simple example of classifying handwritten X and O characters. It provides details on the different layer types, including convolutional layers which identify patterns using small filters, and pooling layers which downsample the inputs.