I cant stop drinking. How can I stop?
You are alcohol dependent, and will need help.  You can't just do it on your own.  Try any AA meetings?
What do they teach you at AA meetings?
They have people who are alcoholics who have stopped drinking.  Their purpose is to "stay sober and help other alcoholics achieve sobriety." Go to a meeting!
What happens if I relapse?
Relapse
In medicine, relapse or recidivism is a recurrence of a past (typically medical) condition. For example, multiple sclerosis and malaria often exhibit peaks of activity and sometimes very long periods of dormancy, followed by relapse or recrudescence.
In the context of drug use, relapse or reinstatement of drug-seeking behavior, is a form of spontaneous recovery that involves the recurrence of pathological drug use after a period of abstinence. Relapse is often observed in individuals who have developed a drug addiction or either form of drug
states "Well-supported scientific evidence demonstrates the effectiveness of twelve-step mutual aid groups focused on alcohol and twelve-step facilitation interventions." 
Relationship with institutions.
Relationship with institutions Hospitals.
Many AA meetings take place in treatment facilities. Carrying the message of AA into hospitals was how the co-founders of AA first remained sober. They discovered great value of working with alcoholics who are still suffering, and that even if the alcoholic they were working with did not stay sober, they did. Bill Wilson