To reach the blood (or lymph), a nutrient molecule must pass through an epithelial cell lining the intestine and through a cell lining a blood or lymph vessel. Absorption occurs by a combination of simple diffusion, facilitated diffusion, and active transport which causes differential absorption of nutrients.
As fats are insoluble in water they need to be emulsified into small water soluble droplets so that lipase can act on them. The emulsification is brought about by bile salts. Term peristalsis describes the series of muscular movements in digestive tract which push the food. The term osmosis is used to describe movement of water molecules across semipermeable membrane along the concentration gradient.