Numerous data models were proposed for practical purposes, which pose a great challenge for big data management. Specifying a database query using a formal query language is a typically challenging task. In the context of the multi-model data, this problem becomes even harder because it requires the users to deal with data of different types. It usually lacks a unified schema to help the users issuing their queries, or have an incomplete schema as data come from disparate sources. Multi-Model DataBases (MMDBs) have been developed to facilitate the management of multi-model data. In this tutorial, we offer a comprehensive presentation of a wide range of multi-model data query languages and to make a comparison of their key properties. The tutorial also offers the participants hands-on experience in issuing queries over MMDBs. In addition, we also address the essence of multi-model query processing and provide insights on the research challenges and directions for future work.