Adding artificial light to your natural light scene is a relatively simple technique that you can use to create an image that depicts the scene more dramatically than it appeared to your eyes when you were there.
Natural Light
An Easy and Effective Trick for Natural Light Portraits

Shooting natural light portraits does not mean you are stuck using the sunlight exactly as it is without any modification. You can use modifiers to shape the sunlight to be more flattering, and this great video tutorial will show you an effective way to create such illumination.
A Modern Approach to Film Photography With Flash

Of course, flash photography existed long before the transition to digital. However, most modern film photography is shot in natural light, whether out of an aesthetic desire or because working with flash and film is a bit of a lost art. Nonetheless, just like digital, flash can open up a lot of creative possibilities, and this excellent video tutorial will show you a modern approach to doing so.