Where did the matter come from that was created during the Big Bang?

The universe was made entirely of energy and was extremely hot at the billionth of a second after the big bang. However, during those first few billionths of a second, energy was also condensing into the fundamental constituents of all elements, such as bosons, mesons, gluons, and so forth.

The components that make up each atom's nucleus began to combine to form hydrogen as the energy and the matter it created began to cool.

Since a star's lifespan is inversely proportional to its size, it is likely that the majority of the earliest stars were extremely large. The largest stars burn out relatively quickly, perhaps even in the hundreds of millions of years. This hydrogen in turn formed rotating pools which, as their collective mass increased, formed stars.

Those early giants, on the other hand, most likely all went supernova when their lives came to an end. Supernovae can produce all of the elements on the periodic table; smaller stars can also produce elements at the end of their lives, but only up to element number 6, carbon. All stars that are unable to become supernovae will cease to exist by the time they reach iron, because the mass of the star determines how much fusion can occur.

Massive amounts of energy were released during the Big Bang, and as the universe expanded and cooled, these energies condensed into elementary particles like electrons and quarks, which in turn formed atoms, which in turn formed all matter that exists today.