Tan (Valefor)

You releases a 10 ft. cone of fire in a direction that you are facing. The cone of fire persists every round for the duration of the spell, so long as you uses your action to continue conjuring flame. Creatures that enter the cone for the first time on a turn or start their turn there must succeed on a Dexterity saving throw, taking 1d12 fire damage or half as much on a successful save.

At Higher Levels
The damage increases by 1d12 and cone size increases by 5 ft. for every other spell slot spent above 1st. If a spell slot of 5th level or higher is used, maintaining this cone requires your bonus action rather than your action.