The question is really way too imprecise, but fusion joins two nuclei together to form one heavier nucleus. The mass of the new nucleus is less than the sum of the two nuclei that were fused...
Nuclear Fusion .
-From Wikipedia (see Web Links to the left):
Nuclear fusion is the process by which multiple atomic particles join together to form a heavier nucleus. It is accompanied by the...
Sun is a star and all stars are big balls of gas, primarily made up of gargantuan amounts of Hydrogen and Helium. To know what is nuclear fusion and how does it work in the Sun, one must know what...