As a simple addendum, the key issue is seperating VFR/IFR and VMC/IMC.
As I'm sure you can recall from your course VMC are the visual conditions allowing flight where navigation by ground features and aircraft avoidance can be achieved using the mk1 eyeball. IMC is weather which precludes VMC.
Therefore it follows that VFR must take place in VMC weather. Navigation can be by any means, including visual, radio aids, gps and ILS if you so desire. The only issue is that an ILS approach is classed as an instrument approach so can't be used in anger ie. there is nothing to stop you dialling up the ILS and having it as the backup to your visual flight but the weather wouldn't need you to use it as your sole navigational aid.
IFR is either procedural due to airspace type and a required navigational accuracy (eg. class A airspace on a gin clear VMC day) or due to weather being below VMC. In both cases, the navigation will utilise non visual navigational equipment, VOR's, NDB's, GPS and so on.
Regards,
VFR