Vata Dosha is composed of air, and space, which is very movable. Within the body this shows up as the movements of food through our digestive system, and our nervous system (but not only).
Pitta Dosha is composed of fire and some water, and in our body is the process of transformation (because fire transforms one thing to another). This is mostly seen in the breaking down of food into metabolic materials.
Kapha is composed of water, and earth, and in our body shows up as structure, support, and our immunity or overall strength.