Back in the 1970s, marijuana was commonly referred to as a "gateway drug" by law enforcement officials and some doctors. It meant that a lot of heroin or cocaine addicts had started on their road to drug abuse by first trying marijuana. They liked the high from marijuana so much that they were inspired to try stronger drugs more often.
"Gateway drinking" is a similar term. It refers to folks who start out only drinking beer or alcohol on the weekends. They like the feeling that booze gives them so much that they eventually start drinking on Tuesdays and Thursdays as well. Before long they're drinking every night of the week and are on the road to alcoholism.
Like the gateway drug theory with marijuana, the term gateway drinking is considered by many to be no more than a scare tactic. Yes, some people who smoked marijuana went on to get addicted to heroin, but a lot of people didn't. Just like weekend drinking; not everyone who enjoys spending Saturday nights getting roaring drunk at the bar ends up as an alcoholic.
Student or Learner