Wood

Wood as a biofuel
Wood is probably the first ever used biofuel. It can generate heat and light when burned. Wood burns because it contains carbon, hydrogen, and oxygen that burn in oxygen. Unlike animals, wood is a good fuel because it naturally contains little water, which inhibits the flame from burning. This is why humans, who are nearly 60% water, will not burn down to the ground if thrown in a fire (they may die, but not be reduced to ashes).

How can we use wood?
Wood can burn for long durations of time, and could replace coal in coal power plants or heat certain objects, such as charcoal in a barbecue or glass in a glass factory.

How it's used as a biofuel today
Wood is being burned often naturally in wildfires, but for thousands of years it has been used by humans. People use wood to heat their homes. Boiler systems are very popular for heating since they are 80-90% efficient, and do not create smoke. Wood is processed into charcoal which is used as a high grade fuel for cooking and heating. Wood and charcoal are both used in a gasification system, which which the produced gas can be used in Central Heating and Power (CHP) systems which uses a similar process as a wood boiler system. The produced gases can be used in internal combustion engines (ICE) as a fuel for generators or automobiles. Wood also produce an oil during the biochar process which can be upgraded to a transportation fuel. Cofiring wood with coal is fairly common, Saint-Gobain Glass's Renedo plant in Spain has partially replaced burning gas with wood from timber residue.

Disadvantages
Burning wood in a fire releases smoke composed of carbon, tar, and ash. However, burned in a low oxygen environment such as gasification, it doesn't produce smoke and is 80-90% efficient. This is harmful to the atmosphere and living beings. Also burning wood means cutting down trees, while today deforestation is a big issue unless we use timber residue or dried leaves, this problem can not be avoided. Planting more trees that grow fast and are able to be coppiced and easily harvested into biofuel is a better answer. There is already commercial grade equipment on the market capable of doing this.