During the process of nuclear fusion in the Sun, the process fuses the nucleus of two atoms.
The sun and the stars create their power through the process of fusion. In this process, two hydrogen atoms fuse with each other or get combined to form a helium atom. While a portion of mass of hydrogen atom is fused with the other, another portion of that mass converts into energy.
To obtain enough energy to fuse with each other, the atoms of hydrogen get heated enough. This occurs with the help of gravity of the sun. It creates a microwave-like environment with high temperature. This way, they get ionized for fusing with each other.
