During a fire, the air around it becomes heated. The heated air sweeps up water vapor (molecules of water that float in the air) and tiny specks of the fuel (the material being burned) into a dark cloud of smoke. If the temperature gets high enough, these compounds burst into flame. Once they start burning, there is no smoke because the hydrocarbons are turned into carbon dioxide and water (both invisible) when they burn.
The more incompletely something burns, the more smoke it produces, because more particles are left to be swept up into the air. Smoke gradually spreads out and drifts away.
The more incompletely something burns, the more smoke it produces, because more particles are left to be swept up into the air. Smoke gradually spreads out and drifts away.