The practice of seeking knowledge of the future or the unknown by supernatural means. (courtesy Google definitions)
First of all, there is nothing "super"natural about it. It is a perfectly NATURAL occurance.
Divination is as defined above, but the methods are widely varied from culture to culture, and user to user. Some examples are Tarot, tea leaves, Ogham sticks, runes, and endless others.
The "skill" of divination is a developed intuition. Whatever practice one uses, the meanings of certain things are not always "black and white" or contained in the little book that came with your "kit".
Developing your intuition is amazingly valuable in many aspects of life and magick, but is specifically useful to Divination.
Also, you should know the suffix "-mancy", as in cartomancy. This suffix indicates that the root word is being used as a tool of divination.
For example, "necromancy"..."necro" being corpse or death, coupled with "mancy" is understood as divination by the dead or using spirits of the dead for discovery.
Hope you learned something here.