When soap is at the surface of water , the hydrophobic ' tail ' of soap will not be soluble in water and the soap will align along the surface of water with ionic end in water and the hydrocarbon ' tail' protruding out of water. Inside water, these molecules have unique orientation that keeps the hydrocarbon portion out of the water. This is achieved by forming clusters of molecules in which the hydrophobic tail are in the interior of the cluster and the ionic ends are on the surface of the cluster . This formation is called micelle.
Micelle will not form all type of solvents. It will form in such type of solvent in which soap is soluble.
eg :- soap in ethanol , hence , no micelle formation takes place.

Micells are the particles that cannot from in the solution of soap in hard water(Ca and Mg)but in detergent solution they are formed and easily clean the dirty clothes