This is an online tutorial where you can learn how to write tool wrappers and workflows using the Common Workflow Language (CWL). The materials provided here describe the first stable version of the CWL - Version 1.0. The tutorial is hosted on the ELIXIR-SI eLearning Platform (EeLP). The main part of the tutorial are learning materials with instructions how to use the CWL to write your workflows. These materials start with the most basic lessons and then continue with more advanced topics, so no previous knowledge about the CWL is required to follow this tutorial.