Extensible Languages and XML comprise a set of tools used to encode, store, and transport data across diverse platforms. Coursera's Extensible Languages and XML catalogue teaches you about XML’s syntax and structure, how it operates with extensible languages, and its wide-ranging applications in data interchange. You'll learn to design and implement XML schemas, understand the role of namespaces, and manipulate XML documents using languages like XPath, XQuery, and XSLT. This skill set can aid you in web development, data science, and various IT-related roles, enhancing your ability to handle complex data structures effectively and efficiently.