The theory behind fusion is really simple. Here is an oversimplification: Take two Hydrogen atoms and squeeze them together until they form a Helium atom and give off the excess energy as heat. Stars do it with massive amounts of gravity from the massive amount of Hydrogen they contain. Scientists don't have the luxury of massive amounts of gravity so they try to achieve the same thing using magnetism, or high voltage, kinetic energy or explosive energy. Hydrogen atoms do not want to change into Helium atoms. They will resist that change with all their atomic might. Now Scientists in several countries have achieved fusion reactions on a grand scale, the 'Hydrogen Bomb'('H' Bomb). This reaction requires a Fission ('A' Bomb) bomb to get it started, and it releases a lot of energy:
Wiki: In May 2023, the United States Department of Energy (DOE) provided a grant of $46 million to eight companies across seven states to support fusion power plant design and research efforts. This funding, under the Milestone-Based Fusion Development Program, aligns with objectives to demonstrate pilot-scale fusion within a decade and to develop fusion as a carbon-neutral energy source by 2050. The granted companies are tasked with addressing the scientific and technical challenges to create viable fusion pilot plant designs in the next 5-10 years. The recipient firms include Commonwealth Fusion Systems, Focused Energy Inc., Princeton Stellarators Inc., Realta Fusion Inc., Tokamak Energy Inc., Type One Energy Group, Xcimer Energy Inc., and Zap Energy Inc.[263]