How many people were on Earth when Adam and Eve were created and their private parts became apparent to them, so they began to cover themselves with the leaves of Paradise?

If you mean the human inhabitants of the Earth, then Adam and Eve are the origin of all humanity. There were no humans on Earth when Adam and Eve were created until they descended to Earth. Allah Almighty said: "It is He who created you from one soul and made from it its mate that he may find tranquility in her." The "one soul" refers to Adam, and "its mate" refers to Eve. Based on this, there were no human inhabitants on Earth at that stage except for Adam and Eve.