2024 rules reference for Alchemist's Fire.
When you take the Attack action, you can replace one of your attacks with throwing a flask of Alchemist's Fire. Target one creature or object you can see within 20 feet of yourself. The target must succeed on a Dexterity saving throw (DC 8 plus your Dexterity modifier and Proficiency Bonus) or take 1d4 Fire damage and start burning (see “Rules Glossary”).