Front lighting is an easy form of portrait lighting. It is also the least dramatic and the most predictable. To create front lighting, the light needs to be coming from the from of the subject.
http://www.digitalcameraworld.com/2013/04/15/photography-lighting-take-control-of-natural-light-to-using-flash/
Side lighting:
Side lighting creates a more dramatic form of portrait lighting. It create contrast between the subject and the background. It also creates more interesting texture.
https://sukis12ymphoto.wordpress.com/page/3/
Back lighting:
Back lighting makes the subject darker and can create a dramatic effect. If the light source is directly behind the subject, the subject can become a silhouette.
http://www.digital-photo-secrets.com/tip/2627/front-light-vs-side-light-vs-back-light/
Top lighting:
Top lighting creates a sense of drama in the photograph.
http://www.diyphotography.net/lighting-techniques-things-can-one-speedlight/
Bottom lighting:
Bottom lighting gives the photograph an eerie sense.
http://www.imagesbot.com/Directional-Light-Photography