Braziers are found in the four corners of the Wintertodt's prison north of the Wintertodt Camp. They can be fueled using bruma roots or bruma kindling in order to drain the Wintertodt's energy.
Feeding braziers bruma roots will reward 3x (5 + player's Firemaking level) in Firemaking experience, whilst kindling will reward 3.8x (5 + player's Firemaking level) experience. If the braziers go out, relighting the brazier will reward 6x the player's Firemaking level in experience.
The Wintertodt will occasionally break the braziers; they must be repaired again before use. This rewards 4x the player's Construction level in experience, provided they own a player-owned house.
At the start of the round, and after the brazier has been broken or extinguished, the brazier will need to be re-lit. You must have either a tinderbox or a bruma torch in your inventory (or equipped) to light the brazier.