The elements come from one of three sources. The first source was the BIG BANG that created the Universe 14 billion years ago.

When the big bang occurred, the elementary particles initially were too hot to make any stable atoms... but after a few thousand years, when things cooled down a lot, Hydrogen and Helium got made. The ratio was about 1 He for every 4 H atoms. This is called RIMORDIAL NUCLEOSYNTHESIS.

Then for elements from He to Fe: these elements are made on the interior of BIG stars (bigger than sun). They are stored there until the stars begin to die. At that point they become unstable and shed a lot of mass... they feed elements from Lithium (Li) to Fe iron into the interstellar medium from which new stars form.

Finally for elements from Iron (Fe) to Uranium (U, these elements get made during rare events called supernovae. This is when a really massive star ends its life not in a mild way but in a gigantic explosion. During the few seconds of the SN explosion, all the elements more massive than iron and going all the way up to Uranium (and beyond), get made and spread out into the interstellar medium.

So ponder this: the Fe in your blood was at some point many, many billions of years ago in the center of a star that has since then ceased to exist.

Early in the life of the universe, lots of hydrogen atoms were created through natural physical processes. Even now, approximately 12 billion years after the universe was created, most of the matter in the universe exists as hydrogen atoms. These hydrogen atoms can come together in nuclear processes called fusion, which is the process that powers the sun, and through fusion, heavier atoms such as carbon and nitrogen are produced. These in turn undergo fusion to make even heavier atoms, and it is such processes that created all the atoms in the earth.

According to the Big Bang theory, during the first few minutes after the "beginning," hydrogen, helium, and lithium nuclei formed from the relatively small number of free protons and neutrons that were around. When the universe was around 380,000 years old electrons were able to combine with the nuclei to create atoms Since that time, some of the hydrogen and helium has combined to form stars and galaxies.

The many other elements that we find on Earth were formed in large stars and then released as the stars burned all their fuel and blew up at the end of their lives (i.e. went supernova).