A well-stocked kitchen is one where the cook can decide to experiment at any time and find all the ingredients for the recipe. This obviously excludes really exotic dishes such as, let's say, fried Mopani worms.
A cook who loves to bake will always have flour, sugar, oil, vanilla essence, eggs, milk, baking powder and a few other things that are common to most baked goods. The one who likes to make spicy foods has a wide choice of spices, especially in today's world where anything can be imported from anywhere.
Firstly, it is possible today to buy many spices whole that were previously only available already ground. Although it is very convenient to have ground spices, and indeed the kitchen can not be without them, but most spices benefit from remaining whole and only being ground when it is actually needed. This is due to the fact that ground spices present so much more surface area for oxygen to react with (this is called oxidation) and consequently lose their flavour a lot quicker. Also, the volatile substances that give many spices their flavour are much more readily lost when the spices are ground.
Whole spices:
Here is a list of those spices that ought to be bought and kept whole, if at all possible.
Pepper corns (black, white and green)
Nutmeg
Allspice (pimento)
Cloves
Cinnamon
Cassia (learn the difference between this and cinnamon in many countries whole cassia is sold as cinnamon)
Dried chillies
A variety of whole spices are in seed form, such as:
Caraway seed
Coriander seeds
Cumin seed
Fennel seeds
Fenugreek
Anise seeds
Star anise (totally different in looks and flavour from anise)
Sesame
Cardamom (white, green and black)
Mustard seed (yellow and black)
Vanilla pod
Ground spices:
As said before, it is impractical to expect the cook not have at least a few spices readily ground, especially those that are used on an almost daily basis. Such spices could include:
White pepper
Cinnamon
Coriander (seed, not leaves)
Cumin
Nutmeg.
Turmeric (not really available any other way as it is a rhizome that is dried and powdered for use)
To grind whole spices:
Traditionally spices were ground by mortar and pestle. There are also little spice mills that are sold in eastern markets usually made of brass that can grind almost anything. However, spices can also be ground in an electric spice grinder, or coffee mill. Most spices should be roasted first in a single layer in a frying pan until they start giving off an aroma and turn light brown. Sometimes this makes the grinding a bit easier, but it is best to be guided by the specific recipe for which the spices are needed.
Storage:
All spices should be stored in air-tight containers out of light. Those pretty spice racks with the glass bottles that stand on the kitchen shelf are really no good.