Can I extract a module or a group of highlighted nodes from the network?

Yes. To do this, first select or highlight some nodes within the current network. Click the Extract icon on the left tool bar in the network view window.

Note the extracted network will be displayed in the current network view. It will be named as module# where # is a number (i.e. module1 for your first extraction). You can later access it from the available networks on the top left corner.