喝酒 is a separable verb (离合词) meaning 'to drink alcohol' — it's the general term for consuming alcoholic beverages. When you specify quantity, duration, or a specific type, the verb 喝 and the object 酒 separate: 喝了很多酒, 喝了三杯酒. This is distinct from 喝 alone, which covers drinking any liquid (水, 茶, etc.).