Torch

Torch is the light source every world starts with, and the one that decides where mobs can appear. Hostile mobs need block light to be entirely absent to appear, so a single Torch shuts down spawning across a surprising radius — lighting a cave is less about brightness than about leaving no fully dark spot anywhere.

Running out of coal does not stop you. Burning any log in a furnace produces charcoal, which makes torches the same way coal does, and a stack of logs lights a long stretch of tunnel. A Torch breaks instantly by hand and drops itself, so a trail of them costs nothing to pick back up on the way out of a cave.

They sit on top of blocks and against the sides of most of them, but never underneath, and they do not survive water — a wall torch pops off the moment a flow reaches it, so lighting a flooded cave or an underwater build needs glowstone, sea lanterns or a jack o'lantern instead. A Torch placed beside ice or snow melts it, which is worth remembering before you light an igloo.

Three relatives change the job rather than the light. A soul torch, made with soul sand or soul soil, burns blue and keeps piglins away from a Nether outpost. A copper torch burns green and never oxidises — the copper is fuel rather than structure — so it otherwise behaves like an ordinary Torch. A redstone torch is a different thing entirely: a power source that happens to glow, not a way to light a room.