This lecture covers the SARSA algorithm, a powerful on-policy algorithm used in reinforcement learning. The sequence 'state-action-reward-state-action' is crucial for updating Q-values. The lecture explains the iterative update process for Q-values in multistep environments, compares SARSA with the Bellman equation, and provides practical examples of applying SARSA in a one-dimensional environment. Additionally, it discusses the convergence of SARSA and the importance of exploration in reinforcement learning.