The Functions Nodes allow the user to create their own Nodes, customizing the Input and Output Sockets and the operation performed by the Node.
Functions can be created in the Functions tab on the left panel of the Logic Editor with the Add Function option and then the Node will appear in the Toolbox.
Each Function has its own Logic, which is defined by the user. This Logic has a Function Input and a Function Output Node, and any other Node can be added to it. To open the Function's Logic tab, either double click the Node or the Function on the Function's list.
Functions can be exported and then imported in a different Project.