On this video, photographer Daniel Norton from Adorama demonstrates how he shoots a model using one or two lights both in the studio and outside and what are some of the differences.
When you are shooting outside you typically have the benefit of an extra light (sun/moon/street light) but in the studio you will typically need to supply your own lighting (unless you have a large lit window).
The first set-up is very classic in the studio with two lights – Norton start with his model and no light – in this situation you should optimally getting a completely black image. Now you can start by adding the first – main light and than the second back light – kicker – to add a bit more separation.
The second part of the video takes place outside and Norton decides to use only a single flash with a softbox and he demonstrates how changing the direction where the artificial light comes from changes the look of the image.