The first possibility is to add and arrange it already at the design time directly in the Composer window. This is a convenient approach you doesn't need to implement a single line of code. See the 'EmWi Tutorial - Mosaic 2.0' chapter '5. Creating more complex GUI components' and chapter '6.2 Composing the Application at the design time'. In this case you drag with the mouse the GUI component (your group) into the root object and Embedded Wizard generates automatically all the code needed to make the group visible in the root object. This approach is very simple and allows you to design a GUI application very easily.
The second way is to create and make visible the GUI Component dynamically at the runtime. This way of creating UI components is explained in the Tutorial chapter '6.3 Composing the Application at the runtime'. Overall, this approach gives you much more flexibility, because you can modify the entire GUI composition at the runtime.
Finally, you can use the view 'Views::Group'. With this view you can show a 'live copy' of a GUI component on the screen. Even several parallel copies of one and the same component can be shown at the same time! Technically seen, this view shows the image of an internally used off-screen buffer of the group. To use this view you need to connect it with a group to show and activate the off-screen buffer in this group. If you are interesting in this aspect, take a look at the description of the class 'Views::Group' in the 'Mosaic 2.0 User Manual'. With the cousin of this view, with the class 'Views::WarpGroup' you can even show a group as a 3D projection.