<human>:  Help me understand the process of nuclear fusion.
<bot>: Nuclear fusion is a process in which two or more nuclei combine together to form a single, heavier nucleus. This process involves the release of energy, and is responsible for the tremendous energy output of stars like our Sun. The fuel required for fusion reactions is usually a combination of hydrogen, in the form of a gas or plasma. In this process, two small nuclei are brought together and combine to form a larger nucleus with a lower energy state, resulting in a release of energy. The heat released can then be used to generate electricity or provide thrust in spacecraft.