Hi,
A couple of additional techniques to those already mentioned:
If you want to group nodes you've already created you can select them in the network view and then choose Group from the Edit menu, or use the ctrl-G (Windows) or cmd-G (Mac) shortcuts.
Another way to enter the internal network of a node so you can create nodes inside it is to context click on the node in the network view and choose "Internal Network" from the context menu.
Regards,
Jo