Micelles are a very beautiful result of some relatively simple chemistry in biological systems. Micelles are made out of amphiphatic lipids, that is to say, a lipid (biological molecule) that possesses both hydrophobic - water fearing, and hydrophilic - water loving areas. In possessing both of these qualities, a hydrophilic head and a hydrophobic tail, when a critical amount of these molecules are added to to water, they will form micelles.
If less than the critical amount of the lipids are added, then one will find a higher concentration of single units of lipids, but at the critical amount or over, one will find a very low concentration of single units.
Micelles find their biological use in the cells of living things. In humans in particular they are essential in aiding in the absorption of fat-soluble vitamins and other complex molecules.