Cashew nuts are not nuts actually, but seeds in a kidney shaped fruit in the end of a "false" pulp fruit called cashew apple. This pulpy part is used for instance for drinks.
Cashew tree has a home in tropical countries.
If you find it somewhere in the nature, you can eat the cashew apple, which is nice and sweet. But do not touch the kidney shaped fruit, as the shell contains very agressive acid and toxins which will etch your skin and can cause other problems. This acid and toxins are removed while processing.
Cashew nuts are used as a snack, in baking or as a part of various recipes, for instance in Thai cuisine.
Recipes with cashew nuts.