The fresher and the more recently ground the roasted beans, the better the taste. Ready ground coffee really only tastes fresh for a short time, because the essential oils begin evaporating immediately the beans are ground and exposed to the air.
The only way to grind roasted coffee beans is in a coffee mill. Coffee mills are based on the principle of mill stones: two flat plates with corrugated faces that crush the beans evenly between them as they are forced through. True coffee lovers do not like the kitchen blender style of grinder as these cut the bean rather than evenly milled the beans.
The types of grind depend on the type of coffee you are making.