This is a great question. While energy is always conserved, its form is not, allowing energy to be converted between different types and harnessed; this conversion between types is fundamental to our universe. If we consider a piece of paper, sitting on a table, it contains energy stored in the bonds between its atoms. Heat can be generated or produced by converting the energy stored in the chemical bonds into heat through a combustion reaction. By setting fire to the piece of paper, its carbon atoms will react with oxygen in the air to form CO₂, releasing energy in the process in the form of heat.