A potency of 2M means a dilution of 1 part in 1,000,000. Homeopathic medicines are not simply diluted. To make a 12x dilution, one drop of the mother tincture is added to 99 drops of the alcohol or water mix and the mixture is shaken vigorously. Then one drop from this mixture is mixed with 99 drops of the dilutant and the mixture is shaken vigorously. The process is repeated a total of 6 times to get a potency of 12x.
Homeopaths believe that shaking transfers the medicine's essence to the water used to dilute it.