Extinguishers are used to put out fires before they get out of control. A full extinguisher can extinguish 10 fires (tiles) before being consumed.
To use an extinguisher, it must be in the player's main inventory, then right-click near the fire and select "Extinguish Fire" from the contextual menu. This will bring up two circles, a large green/red one, and a small white one. The white circle indicates where the player will move to extinguish the fire. The larger circle will appear green if it's in range of a fire and red if it isn't. Any fires in range of this circle will appear red which has an area of effect equal to 4 tiles, therefore the extinguisher can extinguish up to 4 fires at one time.
It is possible for the player to extinguish themselves when on fire, simply include them within the large circle.
Extinguishers are found in kitchen counters, sheds, garages, bakeries, cafes, storage units, gas station counters.