The document introduces convolutional neural networks and how they are used for image recognition through a series of examples using simple arithmetic operations on matrices to represent images and applying filters. It explains how convolutional neural networks use convolution layers to apply filters to images to extract features, pooling layers to downsample images, and fully connected layers to classify images. The networks are trained on labeled image data using gradient descent to minimize errors and improve the ability of the network to accurately classify new images.