Here's a breakdown:

* Oxygen: Capillaries deliver oxygen from the lungs to the cells, where it is used in cellular respiration to produce energy.

* Nutrients: Capillaries deliver nutrients like glucose, amino acids, and fatty acids from the digestive system to the cells, where they are used for building and maintaining body tissues.

* Carbon dioxide: Cells produce carbon dioxide as a waste product of cellular respiration. Capillaries collect this carbon dioxide and transport it to the lungs for exhalation.

* Waste products: Capillaries also collect other waste products from cells, such as urea (from protein breakdown) and lactic acid (from muscle activity), and transport them to the kidneys and liver for elimination.

In short, capillaries act as the vital link between the bloodstream and the body's cells, ensuring the delivery of essential substances and the removal of waste products.