There are two ways to create SubDevice (as well as Widget, Remote, Actions, Events and Conditions): with the help of the editor and with the help of scripts (see the methods in lite API). The editor is recommended when you know the number of SubDevices in the module beforehand (the static module) and this number is not big. Script is recommended when there are a lot of SubDevices and their manual adding in the editor will take a long time. Or when there is no information about the number of SubDevices in the module and it can vary (the dynamic module).