M,
Suggest you stop by a bookstore or library and check out a book on lighting. The basics of lighting are the same now as years ago, so the book doesn't have to be the newest one published.
When you see a diagram, it will make MUCH more sense. Start with a line from the model to the camera. Other lighting will reference this, ie. a main light at a 45 degree angle means a light coming from that angle to the right (or left) of the camera. This 'main' light may be one of several types, for portraits, usually a large light source like a soft-box or umbrella will likely be used, though there are lots of variations. Then you will often use a 'fill' light to reduce harsh shadows from the main light. Next, add in a hair light and another for the background and you are getting somewhere.
Sound confusing? That's why you want to check out a book, or even this link to one of several info articles on THIS web site.
http://www.garageglamour.com/tips/light.php
Also, look closely at the photos you see on this site and try to figure out what the light set-up was. Pay particular attention to the catch lights in the eyes. You can often see where and what kind of lighting was used.
Sorry the answer is so long -- again, pick up a book on lighting. It won't take long for you to understand the lighting effect that the photographer is trying to make. Good luck.
Tom
