Most of the matter in the universe is of which element?
How and where do elements more complicated than this form?
Is this correct?
Helium; more elements are form in the sun by nuclear fusion.
This may be interesting reading for you.
http://map.gsfc.nasa.gov/universe/uni_matter.html
Actually, helium is not the element that makes up most of the matter in the universe. The element that dominates the composition of the universe is hydrogen. Hydrogen makes up about 75% of the elemental mass in the universe, while helium makes up around 25%.
Now, let's address your second question about how elements more complicated than hydrogen and helium form. The process responsible for the formation of more complex elements is called nucleosynthesis. There are two main mechanisms involved in nucleosynthesis: stellar nucleosynthesis and supernova nucleosynthesis.
In the case of stellar nucleosynthesis, elements heavier than hydrogen and helium are formed within the cores of stars through nuclear fusion. This occurs when hydrogen atoms combine under the intense pressure and temperature conditions in the stellar core, forming helium. Further fusion reactions can take place, creating progressively heavier elements. This process occurs during the different stages of a star's life cycle, from its birth in a molecular cloud to its death as a supernova or white dwarf.
Supernova nucleosynthesis, on the other hand, involves the explosive death of massive stars called supernovae. During a supernova explosion, the enormous energy and pressure cause the fusion of elements to occur at a much higher pace. This leads to the formation of even heavier elements, including those beyond iron, such as gold, lead, and uranium.
So, to summarize, while helium is not the most abundant element in the universe, it is indeed formed through nuclear fusion in the sun and other stars. However, the production of elements heavier than helium occurs through stellar and supernova nucleosynthesis processes.