Drinking in Korea is a social ritual with a structure. The rules are few but they are real.
Soju is the default — a clear grain spirit, usually around 16–17% ABV in the standard green bottle, sold cheaply and drunk in small glasses. Beer (maekju) is the other half of the pair. Mixed together they make somaek. Makgeolli is a cloudy, lightly sparkling rice brew at about 6%, served in a bowl and traditionally drunk with savoury pancakes.
Anju (안주) means food eaten with alcohol, and most drinking places require you to order some. This is not an upsell — it is how the venue is licensed and how the meal is structured. Fried chicken with beer (chimaek), jokbal, and grilled offal are all anju categories with their own dedicated restaurants.
You do not fill your own glass. Watch for empty glasses around you and fill them; someone will do the same for you. When a senior person pours, hold your glass with both hands, or with your left hand supporting your right forearm. When drinking in front of someone much older, turn your head away from them as you drink.
A night out moves in rounds — 1차 (first round) at a restaurant, 2차 at a bar or pub, 3차 sometimes at a noraebang (karaoke room). Leaving after the first round is entirely acceptable, especially for visitors. Declining alcohol altogether is also fine; ordering a soft drink is not treated as a problem.