Lighting dark areas
Use light to stop creatures spawning nearby.
Creatures spawn in unlit cells. Place torches in rooms and tunnels to stop new creatures spawning there. A creature that spawned somewhere else can still walk into a lit room.
You can make four torches by hand from 4 Wood + 1 Coal.
Where to put torches
Place torches as you dig. Light the room you are working in as well as the path to it, including any dark pockets behind you. Check the floor and ceiling in far corners: light gets dimmer with distance, so a torch near the middle of a room may not reach them.
Walk through your base and check for unlit cells before you leave. Creatures that spawn there while you are away may still be there when you return.
Torches are not the only lights that count. Drones, pedestals, and worn lanterns also prevent spawns in the cells they light. Pressing K changes whether the lighting is drawn on screen; it does not turn off the lights or their effect on spawning.
Some creatures spawn on the surface at night. The "Found" column in the creature index shows where each one appears.
Once you have light where you need it, Making fire covers the heat you need for smelting ore.