Information processing theory describes how learners receive and process information through their senses. It involves stages of encoding, storage, and retrieval of different types of knowledge in various memory stores like sensory register, short-term memory, and long-term memory. Key aspects of the theory include how attention filters incoming information, the role of executive control processes like forgetting through decay and interference, and methods that can aid retrieval from long-term memory such as rehearsal, organization, and visualization.