Fire

Fire can be started by placing a Stick or Staff on the ground and Pummelling it while holding another Stick or Staff. Using Staffs makes it easier to start the fire.

Any flammable node orthogonally adjacent to a Fire node will/may start burning itself. Once the node starts burning it turns into "Burning Embers" and all empty spaces orthogonally adjacent turn into Fire nodes.

Since the Stick/Staff used to start the fire turns into Fire itself, the initial Stick/Staff should be placed orthogonally adjacent to some Flammable nodes. Loose Leaves seems to work best, especially if two or more are used (it can be up to four, though three allows easier positioning to start the fire).

Once a Fire is started, flammable nodes can be placed in a diagonal grid / checkerboard pattern due to the way the fire spreads. This will allow the nodes to fully burn. Placing flammable nodes too close together can prevent some of them from burning (due to having no empty space around) and then they will/can produce Charcoal (Impure) instead, of various qualities, which can be broken into Ash Lumps and Charcoal Lumps.

Fire can be used to smelt certain materials such as Sand, by keeping multiple Fire nodes adjacent to the smeltable node for long enough.