Machine learning is an area of AI concerned with automatic learning. Some ways ML can be used in expert systems include increasing inference efficiency, testing the knowledge base, and acquiring knowledge. The ID3 algorithm constructs a decision tree from a set of examples to derive production rules, aiming to find a small tree efficiently. It selects the attribute with the highest information gain at each node to minimize uncertainty. However, ID3 has limitations such as handling noise, continuous values, and verifying rules on a full dataset.