Due to the fusion, it emanated to formation of light elements such as—hydrogen, deuterium, helium (two isotopes), lithium and trace amounts of beryllium.
The temperatures in the early universe were so high that fusion reactions could take place.
The reaction chain continues when a massive star runs out of fuel which causes the pressure to drop that leads to a supernova explosion. Then there are two processes of neutron capture called rapid process (r-process) and the slow process (s-process), and these lead to formation of different elements.
In a supernova explosion, neutron capture reactions take place (this is not fusion), leading to the formation of heavy elements.