To understand what energy is created by burning wood, one must first look at the two basic types of energy: potential energy and kinetic energy. Potential energy is defined as any type of stored energy, while kinetic energy is found in movement. Kinetic energy can be seen on many scales, whether it's the vibrating of atoms generating heat, or long wavelength radio waves. When looking at energy it is important to look at the law of conservation of energy. This physics law states that energy cannot be created nor destroyed, but can only change from one form to another (i.e. turning from potential energy to kinetic energy). In the case of burning wood, stored potential energy (in the form of chemical energy) in the log is released due to heating by other excited atoms. This chemical reaction is called combustion and requires oxygen. Combustion changes the potential chemical energy into kinetic energy in the form of heat. For combustion an organic (wood in this example) combines with oxygen already in the air and undergoes a chemical reaction that gives off carbon dioxide, water, and energy in the form of heat and light. This kinetic energy releases in the form of heat from stored potential energy (also some light energy is given off thus we can also see fire). This is why burning wood has been used for generations to heat homes and roast marshmallows on camping trips. Hope this helps!