When you take the Attack action on your turn, you can replace one of your attacks with an exhalation of magical energy in either a 15-foot Cone or a 30-foot Line that is 5 feet wide (choose the shape each time).
Each creature in that area must make a Dexterity saving throw (DC 8 plus your Constitution modifier and Proficiency Bonus). On a failed save, a creature takes 1d10 damage of the type determined by your Draconic Ancestry trait. On a successful save, a creature takes half as much damage.
This damage increases by 1d10 when you reach character levels 5 (2d10), 11 (3d10), and 17 (4d10).
You can use this Breath Weapon a number of times equal to your Proficiency Bonus, and you regain all expended uses when you finish a Long Rest.