This paper describes an effort to provide automated support for the interactive inquiry and explanation process that is at the heart of software understanding. A hypermedia tool called I-Doc allows software engineers to post queries about a software system, and generates focused explanations in response. These explanations are task-oriented, i.e., they are sensitive to the software engineering task being performed by the user that led to the query. Task orientation leads to more effective explanations, and is particularly helpful for understanding large software systems. Empirical studies of inquiry episodes were conducted in order to investigate this claim; the kinds of questions users ask, their relation to the user's task and level of expertise. The I-Doc tool is being developed to embody these principles, employing knowledge-based techniques. The presentation mechanism employs World Wide Web (WWW) technology, making it suitable for widespread use.