Because the Earth does not have massive gravity to fuse Hydrogen atoms the way it happens in Stellar Nucleosynthesis, we rely on two key differences to create fusion reactions on Earth. First we use different Fusion Fuels with Higher Reaction Rates, which are more likely to fuse when they collide, and then we expose them to The Extreme Conditions Needed to Produce Fusion Reactions.
There are several non-energy Scientific and Military Applications for Fusion Reactions. Commercial Fusion Energy Production seeks to capture the energy from fusion reactions and convert it into electricity.